Out of Character
Backtagging/Slow tagging: Always. I can run slower than molasses myself sometimes so slow-tagging is my jam.
Threadjacking: Ask first but it probably won't be an issue.
Breaking Forth Wall: I'd really rather not but if the situation calls for it I could get behind it.
Triggering Subjects: When in doubt, ask? It seems to be the best policy. Things I will not write: Non-con/Dub-con, underage shipping of any kind, guro and other extreme subjects.

In Character
Hugging: Go for it! Iruka is a very hands-on and affectionate person and loves giving and receiving hugs. It sort of goes with the whole sensei to a bunch of mixed-up pre-genin kids.
Kissing: You're welcome to try but he might not reciprocate.
Flirting: By all means. He might flirt back or he might not depending.
Shipping: Sure! m/f or m/m is good for me if it makes sense. We're never given any canon say-so either way about which team Iruka bats for so I figure we can make it up as we go along. I will not write him in a relationship with one of his students because...they're kids and Iruka isn't a pedobear, ktnxbai. Seriously though, the power imbalance is just too squicky for me.
Punching/Fighting: By all means! Though Iruka is a shinobi and while he might be just a chūnin, he's proven himself to be rather clever and will definitely put up a fight.
Injuring Character: Be my guest though please talk to me about anything too egregious before hand.
Killing Character: Only if we talked about it first.
Mind Control/Reading: Go head. Though he does come from a world where such things are known about and he might even be able to recognize the signs of mental tampering via chakra.