I got an ban once for telling someone to ignore an troll, apparently that is harassment and warrants a ban.
Got a temp ban over something similar, it's funny how the English forum mods let the trolls run wild while banning people standing up to them. In my case some new rogue asked for advice because he was doing fairly bad in PvP at the start of MoP. Some level 1 started flaming and insulting him, I answered that he should ignore said person because he was trolling and not trying to help and got a 24~ hour ban for it.