A few comebacks:
"What do you eat?"
"Sticks at the moment, once I'm a level 8 though I can live off air."
"Do you have vegan powers?"
"Yes. Stop thinking that."
"Animals eat meat."
"Animals roll in their own urine, do you do that too?"
"It's natural to eat meat."
"It's natural to rape and kill, but I evolved, maybe one day you will too."
“Where do you get your protein?”
“From eating people who ask me that.”
“what do you eat at restaurants?”
My napkin.
“I don’t understand how you can not eat meat.”
“I don’t understand how you can”.
EDIT: This may help too...
http://www.youtube.com/watch?v=Cpmk93jl6AQ&feature=related