Backtagging: Certainly! I do my fair share of this myself, in all honesty.
Threadjacking: I don't mind, as long as it makes sense. I don't want someone jumping into the middle of a serious interaction without a good reason/something important to add.
Hugging: Go ahead! Unless it's practically a sneak attack, he won't react violently, but he'll be confused and awkward.
Kissing: If it's a surprise make-out, he'll hit the person. If it's innocent or friendly (i.e. quick and not on the lips) he probably won't get too embarrassed, but confusion will happen. There are few situations where he would actually give/accept a serious kiss from someone, and it would take a long period of plotting for things to get to that point.
Flirting: Anything but the most obvious flirting will go completely over his head. Go for it. ;)
Starting a relationship: It would take so much plotting, but if you're persuasive I might be willing.
Fighting: Certainly! It would take a lot of effort to get him into a verbal argument, but he's not unwilling to have physical battles, oddly enough.
Injuring: Definitely possible. I'm welcome for injuries up to very severe ones, as long as the fight has led to it reasonably.
Killing: No, not unless it's been planned.
Using telepathy/mind reading abilities: Let me know first, and we can discuss. I'm okay with some situations, but not with others.