Sometimes it's hard to tell a trolling post from a post that differs from the majority opinion on a subject. If a person has always generally held the same point of view on a subject and they are just making that known again, maybe it's irritating but not trolling. Or, even if it's an opinion the group has never heard yet - still, it might be annoying to hear/ read, but it's not trolling. Deliberately antagonizing a person -most particularly when it's aggressive or mean - just for the sake of antagonizing them and belittling them is trolling.
I don't know where the comments are that inspired this thread but generally I don't like to see a "let's call somebody out on a separate thread", thread. Even if it's because of poor behaviour. Besides, then the troll gets a whole thread dedicated to them, if they were trolling for attention - maybe that's better than the 'lolz' they were aiming for. And if they weren't trolling - then they're being trolled, and that's not right either.