Let's not forget the definition of Troll:
"In Internet slang, a troll is someone who posts inflammatory,[2] extraneous, or off-topic messages in an online community, such as an online discussion forum, chat room, or blog, with the primary intent of provoking readers into an emotional response[3] or of otherwise disrupting normal on-topic discussion.[4]"
It's best not to 'feed' this strange creature by responding to its "inflammatory, extraneous or off-topic" comments.
Just leave them to discuss porn sites, if that's what gives them pleasure.