As a man well acquainted with all the amazing properties of too much alcohol, Tony has his share of drunken mistakes to talk about (though to be fair, all of his worst ones have been stone-cold sober). There's only the one he doesn't talk about, really, and it's not so much a secret as it is something that usually comes up in circumstances better suited to other topics of conversation.
He's been fucking Steve for a week - and he says 'fucking Steve', but he mostly means moaning enthusiastically while Steve holds him up against the wall and gives him a great handjob or ruts against him - before the opportunity for him to notice arises.
This is the first time they've actually made it to a bed, and Steve already has two fingers up Tony's ass before he pauses.
"Tony, is that a tattoo?"
"Uh. I'm guessing you're not going to believe elaborate birthmark?"
When he speaks again, Steve's voice is almost too soft to hear. "Is that my shield?"
"Yeah," Tony admits after a pause. "Yeah, it is."
The thing is, when you've just turned twenty-one and you still haven't gotten over a childhood crush on a superhero and you're really, really drunk, getting his symbol tattooed on your ass seems like a great idea. Most people just assume it's patriotic or anti-patriotic or a few have geeked out with him over old Captain America comics, but Steve's relationship with his shield is a little more personal.
"It is technically Stark Industries tech," Tony adds when Steve is quiet for a moment too long. "Steve, say something. Are you really offended? Because when I got it, it was completely out of good feelings about you. I wasn't being a dick."
And that's when Steve flips him over with one hand, the other one occupied with getting his fingers back inside Tony. Steve's last few seconds of prep work are rough, and before Tony has a chance to catch his breath, Steve's cock is filling him up - too much, really, but he's not about to complain, because the look in Steve's eyes is the most amazing thing Tony's ever seen.
Tony almost regains the power of speech, is about to say something, but then Steve thrusts up into him, hard enough to jolt his whole body, then pins him down by the shoulders to keep him still while he does it again. In the back of Tony's mind is a mental note to explain to Steve that a little warning would be nice in future, because he needs his butt to sit on and he's not gonna want to for a while floats around, but it's mostly lost in everything else screaming at him about how fantastic this is.
Steve leans down after a few thrusts, kissing Tony forcefully, greedily as though he wants all of him, and Tony's brain finally kicks in and tells him what he's been missing - Steve thinks the tattoo is hot.
Tony strikes it off his mental list of drunken mistakes and adds it to his list of good decisions, laughing like an idiot as Steve starts sucking bruises onto his neck.
"That's right, baby," Tony encourages, wrapping his legs around Steve's waist to change the angle of his thrusts, torn between wanting to come and wanting this to go on forever. "Mark me all over. I'm all yours."
This seems to be the right thing to say, if the low, needy sound Steve makes is anything to go by. He sucks longer, more gently, taking his time with every mark he makes. Tony hasn't missed that some of them are high enough up that even a turtleneck wouldn't completely hide them, and knowing that at least right now, Steve wants to mark Tony as his for all the world to see is the best reassurance that Tony isn't just a friendly body for Steve to explore the more liberal attitudes towards sex that he seems to think are the most exciting part of the 21st century so far.
Because he is Steve's, really, and he has been since he announced to his parents when he was seven that he was going to marry Captain America one day. Not that he's actually contemplating marriage, yet, but Steve is turning out to be a great maybe-boyfriend for the sex alone.
"Tony, I need... can you..." Steve pants between thrusts. "I need..."
"Whatever you want, baby. Tell me."
"Bite me," Steve finally manages to get out. Tony's orgasm starts as he realises that Steve wants his own mark, and continues while he sucks intently just above his collarbone, high enough that the bruise will peek over the neck of his t-shirt in the morning and everyone will make the connection that their marks are matching.
Tony only notices as he's coming down that Steve isn't bruising, and bites down instead of sucking. Steve stills when he does, gasping, for air before his hips jerk involuntarily and he's coming as well, making short, satisfied little noises and panting until he pulls out and rolls off, chest heaving and skin shining with sweat.
A red-purple bruise decorates his neck, just where it'll be most obvious for being partly hidden. Tony grins at his handiwork and rolls over to rest his head on Steve's shoulder, because he's been looking forward to this since the second time he ended up coming in his pants against the workshop wall with Steve. Which had been about an hour after the first time, because underneath everything, Steve is still practically a horny teenager. Which is another thing Tony likes about him.
"I would never have guessed that a tattoo would be what did it for you. I might have made more of an effort to let you see me naked if I'd known." Tony rests an arm over Steve's stomach, tracing invisible stars on his skin.
"I wouldn't have just pounced on you if I'd seen it earlier, Tony."
"Why not? That's exactly what you did in the end, anyway." Tony grins up at him, running a fingertip around his belly button to make him squirm.
"You didn't object at the time." Steve kisses the top of Tony's head, putting an arm around him to hold him close.
"Still not objecting." Tony yawns and makes himself comfortable.
"You are covered in bruises." Steve reaches out to touch one, fingers gentle on sensitive skin. "Everyone's gonna know what you've been up to."
"Pretty sure they know I have sex regularly. The real shock is gonna be that it was with you."
"I'll have to keep you marked until it sinks in." Steve smiles as he circles the outline of one of the more spectacular love bites. "Just so they know who they'll have to go through if they want you."
Somewhere deep in Tony's chest, he feels something melt. "I can live with that."