I've always been interested in the etymology of words, where they come from and why they are used to describe a specific action.
In fishing, trolling is where one or more fishing lines, baited with lures or bait fish, are drawn through the water.
In mythology, a troll is a devious, ugly creature. They tend to live under bridges and harass passerby's.
So when someone is called a troll on the internet I get a mental image of a devious, ugly creature baiting a community with their words, trying to lure unsuspecting readers to respond and "rise to the bait".
When you see someone post "don't feed the trolls" they're telling you not to respond in a serious manner to the bait postings.
I find trolls entertaining because there are very few things I take completely seriously on the internet.