Why can't you simply ignore it? I can understand the 'itch' one gets to reply to certain comments as I experience it myself. Labelling posters as trolls is purely a personal judgement. If I'd had a pound/dollar for every time I have been accused of trolling I would now be a rich man.
Many a time I have been sucked into long, drawn-out exchanges which I have later regretted but that is my fault, I didn't have to get involved.
Regarding trolling, there is one poster here who constantly lampoons orthodox Catholicism with the sole intention of annoying and antagonising them and quite cruelly in my opinion. We all know who he is yet gets many, many stars and smiley faces. So who is a troll and who is not depends upon where you are coming from.