OUT OF CHARACTER
Backtagging. Yes! Absolutely go for it. God knows I'm slow sometimes.
Threadjacking/threadhopping. Go for it, man.
Fourthwalling. Sure! It makes for funtimes.
ACTION
Fighting.
Injuries.
Killing.
Telepathy/mind-reading.
RELATIONS
Hugging.
Flirting.
Kissing and/or other intimate actions.