Ok, ok, I really want to do this because I've come up with so many of them that I think really fit him! Ok, let's go!
1. He's actually really clumsy. He always trips over things, drops things, breaks things, and loses things. Don't leave him in a room alone unsupervised because something will go terribly wrong. The crew had to learn the hard way. He also has various scars from his clumsiness.
2. He has migraines. He's had to deal with them for as long as he can remember, and they've also caused his mental health to decline. He tries to conceal them when he's around other people because he doesn't want them to worry about him.
3. As well as opera, he loves musicals. The good ones. Sometimes he'll make Hamilton references while he does his tasks or is impostoring. Anyone who understands his references joins in on the fun and makes more references with him.
4. He's left handed. Mr. Cheese doesn't know. I don't know, he just uses his left hand a lot more than his right. At least that's what I've noticed in the GameToons animations. I could make an entire chapter centered around this if I wanted to.
5. He can be really funny when he wants to be. He's made the entire ship laugh on multiple occasions. Also, GameToons Gaming can confirm this as essentially canon.
6. He's done a fair amount of research on astrology. He still doesn't quite believe in it, but he enjoys looking at random posts about it.
7. He has two of everything. That's fact.
8. He secretly LOVES drama. He doesn't generally get involved in it himself, but he absolutely loves to watch it go down.
9. He suffers from Obsessive Compulsive Disorder. I think he shows a few signs of this in AUL. I'm not sure, but I think it makes some sense. It also goes along with headcanon #7 a little bit.
10. He gets magazines for rich people in his mailbox. Like ya know, Fancy Living Digest or whatever it's called. You know, from the Spongebob episode Chocolate With Nuts? Ok, I'm just gonna stop here before it gets too chaotic.
11. He's never eaten fast food. Ever. His father forbade it because "fast food is for commoners." Actually, this could be a pretty good Gentlecheese fic, or just a good fic in general.
I think that'll do it for now. I could come up with so many more tbh. Hope y'all enjoyed!