Trolls are easy to spot, they're big, hairy reptiles with horns and teeth and they want to get as big as they can so people pay attention to them because their mothers didn't hug them enough when they were children.
Though some trolls use camouflage and can be hard to spot. A forum troll is a person who purposely types something to incite annoyance, trying to get people to fall for their trap to create drama and/or make the thread sink faster than the Titanic (hey, several hours is fast for a thread).
(This troll is trying to get people to burn innocent kittens, notice how he is a relatively decent size. He has confidence, but hungers more attention.)
(Feeding the trolls is what he wants, because more food makes him bigger and causes more attention to himself. Now he can gather enough energy to charge his laser and cause some destruction if he gets big enough. This is bad.)
(When you give your attention ELSEWHERE and not to the troll, he grows hungry, and his power saps and he grows smaller and smaller, powerless! This is exactly what they -don't- want, and they will get smaller and smaller until they poof like Pac-Man after being molested by the red ghost.)
Now have fun, and play nice.