A troll is someone who a) lays Flamebait for no other reason than to start a flamewar or b) Tries to waste the time of forum users (as this one appears to be) by asking questions that no-one would normally ask
Kind of a vague definition but that about sums it up.
I've always find Trolling kind of interesting in that (for me at least) the only person truly wasting their time is the Troll. I only ever come on the forums when I have nothing else I should be doing or because I feel like coming on here. If I am programming then the I will only stop to come on the forums if I get a topic reply notification for a thread that I find interesting, or I am stuck on a problem. So Trolling does not waste my time in that i am already in effect wasting it. Not to say that coming on the forums is a waste of time, because its not but you see what I am getting at.
As for the Trolls who lay flamebait I find it kind of pathetic that they have nothing better to do than try to start flamewars (Though reading a good flamewar can be quite amusing). No the thing that P*sses me off is people who try to use forums for Spam and advertising - take for example the 'Phone sales' threads that have appeared a number of times, let alone the spam that appeared in the poll.
Then again that might just be because Spam P*sses me off anyway. Question is why do Trolls bother? is it because they are MS/Mac fanboys? Is it because they have nothing better to do? Do they find it funny? Or is it just that they are grumpy people who live under a bridge
Personally I think it is the last one, the bridge in the metaphor being everyone else being able to use/understand the object in question. It strikes me as coincedental that most Trolls on Linux forums clearly have no idea of how to use it, some don't even seem to know what Linux is.
To sum up a Troll is someone who tries to climb the bridge of understanding and whack those legitemately on/above the bridge on the head