There's a picture of the Avengers, and no matter how many times SHIELD tries to take it down, it comes back. It's true you can never erase anything from the internet completely. Even JARVIS tried once, just for laughs, but failed. Tony told him it was okay.
It's the only image in the entire world that can make both Tony and Coulson twitch. For different reasons, but it still counts.
Tony redesigned the penthouse of Stark Tower after it got thrashed. He tricked it out with bedrooms specifically conceived with the Avengers in mind, and he placed them around a central common area, an open kitchen and dining room divided from the living room by a long counter. There's an actual bar, a pool table, and a long workdesk. There's a home cinema system that would put most professional movie houses to shame. The dining area has a large round table because Tony can't resist Arthurian imagery.
Tony thought he had worked this out to perfection, this idea of the Avengers having a real headquarters. He'd read some book or other about communal spaces in the workplace and team building, and he'd retained enough of it to make a truly welcoming home for his new team.
He realized his mistake the first day after they all moved in, when he surfaced from the lab in the early morning to get something to eat and came face to face (well, face to pectoral) with Steve Rogers, in a pair of boxers, frying bacon.
"Stark!" Steve said cheerfully, waving with the spatula. "This place is great. Thank you. Bacon?"
"Enh?" Tony replied. Because pinnacle of human perfection, frying bacon in his boxers.
"I made enough for everyone," Steve said, and offered him a slice.
Tony took the bacon. Never turn down free food.
"Boxers," Tony added, crunching it up.
"Where are your pants?"
Steve gave him a worried look. "I put them away in my closet."
Tony decided he wasn't awake enough for this conversation, and slunk away to his bedroom.
And he convinced himself the boxers were a hallucination, because the next time he saw Steve Rogers, late in the afternoon, he was getting ready to go to some meeting at SHIELD and was wearing clothing.
Then Thor walked into the living room clutching a large bowl of popcorn, naked as the day he was born. (Were gods born? Terrible question, strike from the record.)
"Ah! My friend, truly, this is a haven for the weary," Thor informed him. Tony thought about keeping his eyes firmly on Thor's face, but he was after all Tony Stark. He glanced down.
"Truly," Tony said, looking quickly back up, "you have a mighty hammer, Thor."
Thor just grinned, ate some more popcorn, and threw himself down on the couch.
"MAN IN THE CEILING. ENTERTAIN ME," he bellowed.
"Loading video," JARVIS replied neutrally.
Tony fled to Bruce's lab. Safe, sane, and clothing-required.
"Hey," he said, as he walked into the lab. Bruce looked up from his microscope and smiled. "Thor's naked in the living room."
"Ah, yeah, Steve's fault," Bruce answered.
"Well, Thor saw him cooking breakfast pantsless -- "
"So that wasn't a hallucination," Tony said flatly.
"You'd have to have a fevered imagination or an exceptionally good grasp of human anatomy to hallucinate that kind of musculature on a human being," Bruce replied. "Anyway, Thor saw Steve in his boxers and said something about being pleased that Midgardian clothing taboos didn't apply in private, and stripped off in the kitchen."
"Did Captain Forties have a coronary?"
Bruce shrugged. "Man went through boot camp. I hear the US Army isn't big on privacy. He didn't seem concerned. Are you telling me you mind?"
"I'm feeling a little intimidated."
Bruce smiled. "He does have a magnificent hammer."
"That's what I said!"
"Well, the joke is there to be made." Bruce turned back to his microscope. "If it's upsetting you, tell him to put some pants on."
"I'm not upset. I am a man who fully approves of nudity. Why, does it bug you?"
"I'm pretty sure Hulk's flashed enough people in this lifetime and I know I've woken up naked enough places that I can never have shame again," Bruce sighed. "I just wear pants because I get cold. Reason I always chose warm, humid climates when I was on the run."
"Can I stay here with you while we both wear pants?"
Bruce patted Tony's shoulder. "There's nothing to be ashamed about, you know. The human body is a beautiful thing."
"I'm not ashamed!"
"Oookay then," Bruce replied. "Come do science with me. I promise to keep my pants on."
By the time Tony came back up to the House Of Waggling Penises (penii? Penes?) everyone was in bed, which was a relief. He considered napping on the couch, then realized he was going to have to ask the cleaning staff do an extra-deep scrub on the upholstery before he'd feel comfortable with that.
In all, though, he felt optimistic. Surely, if Thor saw the rest of them wearing clothes, he would take the hint. He wasn't dumb.
The next morning, a knock on his door woke him.
"What, oh my god, is there a fire?" he asked blearily, sitting up. Clint opened the door.
In his underwear.
Tony gaped at him. Clint was talking, but Tony just stared.
"Are you wearing Captain America briefs?" he asked.
"Yeah, I just said, come watch me make Steve freak out," Clint replied.
"Who's watching you make me freak out?"
"Really? Loki, the Chitauri, nukes in space...and me in Captain America undies freaks you out?" Clint asked.
"Nukes in space make sense. Where did you even get those?"
"Stole them from Coulson," Clint said. "Why, you want some? I warn you, they might be vintage."
"No! Go away, I need nine million more hours of sleep."
"Your loss," Clint said, but he left the damn bedroom door open, and thirty seconds later Tony heard a crash that surely heralded Steve's reaction to Clint's underwear.
Natasha leaned in the open door. (Upside down, from the ceiling.)
"Move it or lose it, Stark, Cap's making breakfast," she announced.
"Lose it! Losing it!" Tony said. "Shut the door. Everyone's naked all the time!"
"I know. It's fantastic. Spank-bank fodder for months," she replied, flipping down to land effortlessly on her feet. "Think we could get Bruce into it?"
"But I like his pants," Tony said faintly.
"No, Pepper, you don't understand," Tony said, when he called her and laid out the problem and she just laughed until she wept. "This is a serious interpersonal issue I am having."
"Tony Stark, undone by nudity. Oh, god, JARVIS, make sure you send me a transcript of this phone call," Pepper said.
"Nudity has a time and a place! Preferably directly before or after sexy times. It ruins everything if you're naked all the time!"
"For them or for you?" Pepper asked.
"Captain America is in his underwear! Constantly! Thor -- I'm going to have to follow him with a spray can of disinfectant."
"Towel," Pepper said. Tony stopped pacing.
"Tell him to bring a towel with him and sit on it."
"How do you...did you just come up with that?"
"I spent a week at a nudist club once."
"Where was I?"
"Employing someone else, I think, this was years ago. My point is, if Thor has a towel, problem is solved."
Tony started pacing again. He was on the terrace, and when he looked through the glass walls to the living area, all he could see was Steve Rogers shirtless, Clint still in the Captain America briefs, and Thor stretching. And Thor's ass, flexing. And Natasha in a sports bra.
"Problem is not solved," he said.
"For them or for you?" Pepper repeated.
"Not helping, Pep, I feel betrayed. I have serious emotional issues and you laugh."
"Tony, you've had serious emotional issues for years, and I have always laughed at them. Get over it. I know you're not uncomfortable with nudity and I strongly suspect you are channeling your massive, hilarious insecurity complex into a concern about the modesty of your new best friends. If you want them to put more clothes on, say so, otherwise strip down and have fun." She paused. "Captain America really makes breakfast in his underwear?"
"Every fucking day."
"I'll be on a jet tonight. I should get there in plenty of time."
"Bye, Tony," Pepper said, and hung up, the vicious minx.
"Tony!" Bruce called, leaning through the doorway. "You'll freeze to death out here. Come inside."
"I have to go get Thor a towel," Tony said resolutely.
In the end, there wasn't really anything for it. It wasn't like he could tell people to put more clothes on, and he didn't even really want to. But Tony had a certain sense of style that did not allow him to go around in less than either suitably rock'n'roll workshop grunge or exquisite tailored designer suits, so once he'd forced a towel on Thor and bought Cap an apron that read NATURAL BORN GRILLER on it and made Clint promise not to be naked in the ventilation system (it wasn't hygenic) he gave up and just tried to lead by example. Even Bruce, who apparently wasn't a fan of belts or shirts anyway, eventually fell victim to the culture of nudity that Steve goddamn Rogers had engendered and Thor had violently evangelized.
After a while, Boxers And Bras Movie Night even became sort of fun. Especially when Pepper was around.
But the problem was that they were, after all, Avengers, and sometimes emergencies happened. Once in a while those emergencies were just fire drills, but someone had neglected to inform Tony that the fire department was conducting a drill in the residential levels that day, for which they would pay dearly. Nobody had bothered to tell Steve or Thor what fire drills in this century and realm consisted of, and so when the drill alarm went off one late afternoon, Thor freaked out and went out the window. Steve literally grabbed Bruce and ran. To their credit, Clint and Natasha valiantly tried to stop him and got dragged along with.
Tony came out of the meeting he was in on the third floor, took the stairs sedately to ground level where everyone was gathered, and found that the mighty Avengers were standing on the street, in the cold, looking confused, surrounded by firefighters, shivering in their underwear.
Tony, feeling as if he ought to be a gentleman, gently nudged Thor's hammer in front of his junk, then shed his suit jacket and held it politely in front of Steve.
Click went every camera-phone on the street.
Steve, who could out-gentleman Tony on his worst day, took the suit jacket, gave Tony a grateful look, and hung it gently around Natasha's shoulders.
"Right now," Clint said, leaning into Tony, wearing a pair of combat boots and (gratifyingly) Iron Man briefs, "Nick Fury is blowing a vein. Can you hear it? I can hear it."
"Not over the ones I'm blowing," Tony replied. "Okay, kids, let's go inside, the show's over."
"But are there no villains?" Thor asked forlornly, waving the hammer.
"No villains, buddy. Bruce?" Tony asked. Bruce, at least, was mostly clothed. "You feelin' green?"
"I'm fine," Bruce said faintly, helping to herd a disappointed Thor back into the building.
The elevator ride up to the penthouse was very, very silent.
"Do you think that'll get into the papers?" Steve asked. Bruce facepalmed.
"It might," Tony said. "It might, Steve."
"That's probably bad," Steve said thoughtfully.
"Why?" Clint asked.
"Aside from the fact that it looked like you were all in the middle of an orgy?" Tony asked. Steve made a soft noise of horror. "See? Now we've all learned our lesson about pants, haven't we?"
"But they chafe," Thor replied.
Tony walked out of the elevator, straight to the bar, and picked up a bottle of Grey Goose.
"I'm getting very drunk," he said. "Anyone who wants to join in should sit their ass down towel first Thor towel first!"