Everything's a process.

The quick and dirty:

[OOC]
Backtagging: Always.
Threadhopping: Ask first, please!
Fourthwalling: Ask first, but I'd probably prefer you didn't.
Offensive subjects: I'm pretty hard to offend oocly. I can't really think of anything to avoid.

[IC]
Hugging this character: Sure.
Kissing this character: Sure, but how he responds depends on who you are/where you try to kiss him.
Flirting with this character: You can try! He does have a boyfriend though.
Smut with this character: I'm fine playing it out or fading to black. He does have a canon boyfriend, but I'm willing to try other ships with him if it can be worked out in a way that makes sense.
Fighting with this character: Sure.
Injuring this character: Ask first!
Killing this character: Ask first!
Using telepathy/mind reading abilities on this character: Ask first!

( In-depth kinks list )