You: Your heart in a blender?
Not a bad comeback, Avarie537, even though the remark really was hideously inappropriate. Given that you have to work with this weirdo, it probably was better than screaming “YOU CREEP!” or whatever.
Another option, for this and for Pullet: Play dumb. As in “What do you mean by that? I don’t understand.” - followed by additional requests for clarification - but only if there are others around to hear the whole thing. i.e., do your best to embarass the person who made the inappropriate remark. Maybe finish up with a mild “I have no clue why you’d make a remark like that”.
I once worked for an eminently hatable boss named Chip. One day, he mentioned where he had grown up. I said, “Really? I thought you were from upstate New York.”
He said, “No, never even been there.”
“Then how come these guys call you Buffalo Chip?”
(For you non-yanks, a buffalo chip is buffalo dung, and Buffalo is a city in New York state.)
Thanks, Large Marge and Mama Zappa, although I like Marge’s idea better. 
The best I’d come up with (hours later) was “What? Oh, you’re an asshole. I don’t take shit from assholes.” I think, if he’s a Troll again, I’ll just calmly explain that if he says anything like that again, I’m going to hit him. So he gets one freebie and one warning. That’s fair, right?
I second the idea of playing like you don’t understand what he’s getting at (I didn’t get it, either - that was incredibly lame of him). I had an obscene phone caller hang up on me once by pretending I didn’t understand what he was talking about until he got too frustrated.
Or maybe just say something like “Is there something wrong with you?” Actually, that would have been a good comeback for the incredibly inappropriate comment in the OP, too.