There are a lot of screwed up people on the Internet. The wisest course of action is to ignore them. The reason he keeps digging at you is because he knows he will get a response. 

Just ignore him. He'll find somebody else to pick on.

I once heard a dog trainer on one of those "Help, my dog misbehaves" shows tell a dog-owner, "From his point of view, you're turning  yourself into a giant squeaky toy, so of course he's going to squeak it."