Here in Canada it means someone who frequently causes trouble or enjoys doing so. I think the BrE equivalent is sh*t stirrer, but I wonder whether the Canadian expression is also used in the USA? @Tarheel@Skrej@Amigos4
Hmm, I'm not sure I've ever heard it used as an agent noun, but I have heard and use 'stir up sh*t'. Extrapolating from that, 'sh*t stirrer' seems more logical than 'sh*t disturber'.