Any comment which contains "you actually don't know your stuff" is uncivil. Personal assessments of other posters are always uncivil. 

A troll is one who posts a deliberately provocative message to a newsgroup or message board with the intention of causing maximum disruption and argument.

For example, were one to encounter a poster whose posts consist primarily of personal assessments of posters with whom they disagree, disparaging of authorities, mocking of public personages, and the like but lacking in citations to actual authorities, logical constructions designed to endorse or question a proposition, questions such as "could you provide an example", one might conclude that poster is posting with the intention of causing maximum disruption and argument.