a. Ignore them.
b. Troll them straight back.
I'd probably just ignore it....mebbe...
but, if i'm in a shitty mood, I may retort with something rather nasty. I'll share one of my faves should anybody else need a good one on short notice:
"Why dont you let go of the keyboard, go outside and play Hide And Go Fuck Yourself?"
"yiff in hell"
There's no sex like succubus sex!
"die in a fire"
'O', is THAT the latest furry fetish? Here I was thinking it had something to do with fursuits.
Why? Does it have your cum in it?