One who has a PhD in Trollology. Different people may define this differently. Here is one definition. Trollology is the study of internet trolls. See Trolling for further info on that. A trollologist studies the habits of trolls in hopes to point out certain characteristics that trolls carry, so that these characteristics are pointed out to the public, thus defeating the goal of internet trolls.
My friend the Trollologist just discovered another way to point out an internet troll. It was very helpful. I managed to point out a troll much easier today.