There is a pretty standard definition of an internet troll, whether or not everyone here will agree, and that is someone who wants to disrupt and who wants to make themselves the topic of the thread. I agree with Jessalonika (i think she hates it when i call her that), that one man's troll is another's droll companion.
If a question is asked, and i has been answered, i consider the thread fair game for silly remarks. If a thread asks a question which is an absurdity--i have the same attitude. If a thread has ongoing status, though, if people are discussing an idea or a topic, and people are jumping in with what is basically "Hey, look at me, look at me," i consider that trolling. Both Jes and i add soundtracks to threads, and i don't consider that too disruptive--after all, one has to click on the post ot hear the music, and it's not necessarily about the person who posted the video--it's about the music, which people are free to ignore.
My comment about LIl Kay's "Atheism" thread came because the topic is about the experience of being an atheist, and the thread is just overrun with god botherers and agnostics. Sure, they have a right to post there--i've always made it a point of saying that anyone can post anywhere, particularly when someone refers to a thread as "my" thread. No, it's not mine, anyone can post there. But in the "Atheism" thread, one of our atheists would post something, and if you replied, there might be four or five posts in between, none of them germane. There are about three trolls there now--one is completely clueless and trolls just about every thread in which that member posts. One is a loony christian who tries to get a rise by posting slighting comments about atheists. One just peddles the same tired bullshit we've heard for over a decade.
And there's one enabler there, too. That's the big problem--people who respond to trolls only encourage them.
Which is, of course, why i so rarely respond to . . . uhm . . . what i mean is . . . hey, look at the time, i gotta run.