There's a very fine line between a jokey troll reply that's fun and an asshole troll reply that can ruin someone's day. I don't quite know where that line is, but for the first type, I can respect it and might even enjoy it and respond/fav/whatever. The second kind tempts me to use the block button.
I usually assume most people are trying to be lighthearted and so I tend to give them the benefit of the doubt but do and say nothing. Still, though, it gnaws at me that I may never know for sure.