Posting in threads that aren't directed to you.
If you see a thread that contains two people talking back and forth, do not comment on it.
This can irritate people very quickly, there is no punishment for this, other than your comment being deleted. People talk on messages walls and forums to work out things, you don't need to put your input in or ask what's going on. Five times outta ten it's not about you or concerns you.
If this continues, a harsher punishment will be in affect.