Fair comment - maybe it's time to work up a clearer definition of the troll than simply looking at the behaviour. I'll kick off ... please feel free to chip in.
1. Knowledge of subject - we all occasionally display amazing ignorance. That's human. Trolls, however, consistently and persistently display utter ignorance of the subject at hand: sexist comments on nurses' groups, blasphemy on religious groups .. I kid you not, and it's clearly no accident.
2. Pedantic in the Extreme - Many perfectly OK human beings can be quite pedantic, but troll posts typically display this trait in order to prevent a serious discussion from advancing. On occasion, it's hard to tell the serious pedant from the troll; but when combined with other features, the troll usually stands out from the crowd
3. Off-topic posting - Often genuine errors, but, if from an 'outsider' they deserve matter-of-fact response; if genuine, a brief apposite response is simply netiquette; if it's a troll post, you have denied it its reward. Again, if this is a repeated behaviour, or combined with other trollish behaviour, it's rarely a mystery.
4. Missing The Point - we're all human, and this can happen to the best of us. But trolls rarely answer a direct question - they cannot, if asked to justify their twaddle - so they develop a fine line in missing the point.
5. Abusive - Few regular forum/Usenet users can say they have never lost their cool; good luck to those who can make that claim! But trolls go from nothing to four letter words with zero provocation, and do so regularly. This is not the case with human beings.
Like most internet bad behaviour, the definition depends a lot on intent; has someone got ratty because they've been unfairly attacked, or are they making fuss about nothing, simply to disrupt the group?
In most cases, human beings will show one, maybe two of these traits; trolls will consistently and repeatedly show many more. On occasion, it's a thin line; maybe a troll is rejoining the human race, maybe a once normal person has given in to the temptation to be a total idiot. But usually, read a couple of posts and the answer is fairly clear
