There are three things in Percival Graves' life that no one is allowed to talk about (well there are many, many incidents that aren't allowed to be talked about, but there isn't enough time in the world to go through all of them). At least not to his face or where he could possibly overhear. These events ranged from his time at Ilvermorny to... very recently, all with one common thread. Alcohol.
When Graves thinks about it, he really should just give up alcohol altogether. Especially in group settings with Picquery. Nothing good ever comes out of it.
There was the incident in fifth year, on Halloween. It had been Picquery's idea to sneak in the firewhisky, never mind that he had agreed first. And so what if it was his idea to play truth or dare (it's a classic Picquery, we had to do it), he had already had more than a few drinks while doing it. They didn't have to go along with it.
But they did, and there he was, standing behind a pillar in the corridor, all of his friends behind him giggling. He was supposed to be spelling one of the professors robes longer so he tripped over them, hopefully into the dining hall. Normally he'd be able to do it, if he wasn't drunk off his ass, but as he was, he ended up hitting the headmaster in the back of the head (had he been walking next to Pinkin the whole time? Huh, what do you know, he was).
His friends had all ran for the dorms when the spell hit, trying to muffle their laughter as the headmaster turned around, furious as hair began to spout out of his head, like he hadn't been bald the second before.
For that gesture of kindness ("honestly headmaster, you look better with all the hair, you should be thanking me" he had slurred as he was dragged to his office), he got detentions for the rest of the year, twice a week. And with Professor Pinkin no less!
But yes, anyone who spoke of that incident got the combined Graves Effect™ as Picquery had so lovingly named it- a glare and a hex that varied, but was always questioned whether it was illegal or not ("Oh he'll be fine, the blood will stop eventually. Honestly, have you never had a nosebleed before? It's like that, but... worse.").
There was of course The office party, as a Junior Auror. Picquery, had proposed the idea for the party, because 'We deserve a little fun every once in a while, don't we sir? Plus you can tell the president that you're working on trust and unity in the department, that'll get you promoted for sure' (it didn't).
Graves hadn't even wanted to go to the party. He didn't particularly like the idea of having to mingle with the rest of the Aurors, as many of them had egos bigger than the new 'skyscrapers' the no-maj's were building. But he was coaxed into going by Mitchell, and the promise of free alcohol.
That was his first mistake that evening. His second, was taking Mitchell up on the offer of firewhisky. His third, was challenging Picquery and one of the newer Junior Aurors, Rey, to who could drink the most.
He blacked out after... well he wasn't sure how many drinks it took for him to pass out, but it was quite a few. To his utter surprise, he woke up, hours later with only his socks on, in the wand permit office. Graves has no idea how he had gotten there, or where the ever loving fuck his clothes went, even to this day. He has a strong suspicion that it was Picquery, as most things often are, but never had any actual proof about it.
Contrary to the incident in fifth year, The Office Party is widely known among the Aurors, to Graves' utter annoyance. Over the years, as Graves climbed up in MACUSA, people have learned to stop mentioning it if he's in the general vicinity, due to his arsenal of gagging spells ("Get your mind out of the gutter Picquery, it's for criminal purposes" "Sure Percy, whatever you say") and his ability to make 'accidents' at office parties happen.
The biggest embarrassment though, only four people, including Graves, know about. Picquery, and Graves' mother and father.
It all started with a misunderstanding. That's all it was. It wasn't his fault that his parents thought that he was dating Picquery. It wasn't even Picquery herself, for a change.
Graves and Picquery have been friends since they were little, and have been attached at the hip, no matter how annoyed they got with each other. It was only natural to have her over at his house all the time- they lived right down the street, and he had cooler stuff to do.
His parents however, saw it differently. As they were unaware, that Graves was and is a raging gay. He still keeps it on the down low now, as not everyone likes that in a person. But anyways, they saw Picquery coming over all the time, as the two of them dating. They never questioned why their darling Percival wouldn't tell them that the two of them were dating, they just saw it as normal couple behavior.
Fast forward years later, after they're out of Ilvermorny and working for MACUSA. Graves is an official Auror at this point, and working towards Director of Magical Security. Picquery is an Auror as well, and is aiming even higher, and is running for President. His parents are getting worried about him though. He's moving up in the magical world, and so is she. Why don't they get married already? Mrs. Graves hasn't even seen a ring on the poor girl's finger! They're not getting any younger, and she wants grandchildren.
Now, whenever Graves visits his parents, he usually brings along Picquery, especially for the holidays. He goes to her house as well to celebrate, as he is very close with her parents and siblings, but that's not all that important in the grand scheme of things, besides cementing the fact that they're dating to his parents.
One Christmas Eve, Graves is sitting with Picquery, drinking some coffee, when his mother and father burst into the kitchen, after a few to many spiked glasses of eggnog. They then proceed to pounce on him about 'when was he going to marry his girl? It's been years since you two have started dating- you better make a move'. Honestly, Graves couldn't say he was surprised, especially when Picquery started laughing.
His parents were more confused than ever when they found out they weren't actually dating and subsequently, that Graves was about as queer as a three-dollar bill. He was absolutely mortified at the revelation coming to light, which is why Picquery is no longer allowed to laugh at his expense about it, without suffering the major Consequences that come with it- like the Graves Glare™ and a mild stinging hex.
There are, of course, more moments than these three, including the incident that resulted in Betty, though the "We don't talk about it rule" doesn't really apply to her. And these three don't even scrape the surface really.