Threadhopping/threadjacking: Ask first, but I'll most likely say yes to it. The more the merrier.
Attack/Injure: Attack him at will, but he's going to fight back. Not so easy to overpower unless you are much bigger than him. Superficial injuries are fine with me, as for more serious ones, please PM me.
Intoxicate: Try it. He's probably a hilariously passive drunk.
Mindfuck/Rape/Torture/Kill/etc.: Mindfuck is an a-okay with me, rape is just a no-no, torturing is fine but I'd like to know in advance what you're planning to do with it, and killing is something that we'd have to talk about. I don't mind killing my character, but I'd like reasons as to how it will progress plot.
Hug/Kiss: Hugging is okay, he won't squirm away or anything unless he really isn't very fond of you. Kissing him will result in a "Huh" sort of reaction, in which case if you were talking to him before the kiss, he will resume the conversation with much awkwardness to be had.
Sex logs: Don't mind playing it out, if you want to fade to black, that's okay too. Just let me know what you want.
Read your thoughts/emotions: Go ahead, but let me know if you want to do this. That way I'll put a bit more detail into what he's thinking so your character can, you know, respond to it.
Anything you don't want brought up to this character? Nothing really? Just don't touch his marker.
Anything else? C'est fini. Fourth-walling will make Yuusei "WTF" and question your sanity. He also just won't believe you. Fool.