A derogatory term describing, and very useful for offending, vegetarian/vegan persons who insist on pushing their beliefs onto other people.
A granolawhore is typically highly pretentious, less than educated on their beliefs (they'll often say that humans can't actually digest meat, and similar nonsense) and is completely oblivious to the fact that the person they're talking to doesn't care about their opinion.
granolawhore: "Why are you eating that? Meat is murder!"
you: "Quiet, granolawhore."