What is the psychology behind trolling?
There are a few references to the scientific literature on trolling in the wikipedia article


  Some psychologists have suggested that flaming would be caused by
  deindividuation or decreased self-evaluation: the anonymity of online
  postings would lead to disinhibition amongst individuals (Kiesler et al, 1984). Others
  have suggested that although flaming and trolling is often unpleasant,
  it may be a form of normative behavior that expresses the social
  identity of a certain user group (Lea et al, 1992; Postmes et al, 1998).


References


Kiesler, S. , J. Siegel and T.W. McGuire (1984). "Social psychological aspects of computer-mediated communication". American Psychologist 39 (10): 1123–1134. doi:10.1037/0003-066X.39.10.1123. LINK
Lea, M., T. O'Shea, P. Fung and R. Spears (1992). "'Flaming' in Computer-Mediated Communication: observation, explanations, implications". Contexts of Computer-Mediated Communication: 89–112.
Postmes, T., Spears, R., &amp; Lea, M. (1998). "Breaching or building social boundaries? SIDE-effects of computer-mediated communication". Communication Research (25): 689–715. FREE PDF