The definition of trolling from the Urban Dictionary:
Trolling is a favorite past time for unhappy and disenfranchised men. There are several factors that contribute to trolling. When these exist trolling becomes a seductive past time for certain types of people.
The online disinhibition effect: The internet creates an illusion of invincibility. Saying things behind a keyboard doesn't have the same consequences as saying it to someone's face. Trolling is the preferred weapon of cowards.
Anonymity When you combine anonymity with disinhibition, the consequences go out the window. This is when the dark-side of humanity appears. The troller feels no connection between what they post to their own life. Therefore they can be cruel and even sadistic online and then go about their day like nothing has changed.
Tribalism Men sometimes behave like pack animals. This is true in online forums when groups of trollers gang up on somebody. If the group is brought together by some kind of idealism they will single out their "opposition" online.
Who are the trollers?
Not all trollers are men. But the vast majority of them are deeply unsatisfied males. They have low-self esteem and feel disconnected. Trolling gives them an outlet for their self-rage. Just like any other bully, when they can make someone feel small they feel bigger.
However, trollers live in a fantasy world. The person they hurt the most is themselves. The wasted time and energy of trolling is a drain on their own resources. The energy it takes to troll should be used to improve their own life.
Changing your life doesn't have to be hard. An improvement of 1% everyday will create massive changes over time.
Sources:
The Psychology of Online Trolling