Trolling is ok as in playing funny tricks on people. But sometimes it is plain bad. For example being afk in a teamwork requiring game isn't really trolling but just being a huge jerk. Like griefing in a minecraft server. I mean, even if you are going to grief, do it with a bit of style. Burning everything up while no one is online is just plain annoying. So the thing is it has to be done cleverly, in an amusing way. Using hacks and killing everyone with one grenade in an fps game is not yay.