i have no problem with any diet, so long as you're not a dick about it.
vegetarians? no biggie. pescatarians? well, i don't like fish, so they can have my share of the stuff. pure carnivores? ok, fine, but don't ask me to follow, i love vegetables too much for that.
vegans? well, they're a bitch to cook for, but if they're not militant about it (ie: "meat is murder" types), go ahead. your body, your rules.
my real only gripe is people who won't try a food because it grosses them out (or they find the animal "cute"). because of that, i didn't try rabbit until my early 20's, because my sister found them too fluffy and cute. and man oh man was i ever missing out. baste the sucker in mustard seeds and and some garlic, you've got an easy feast!
oh, and for the best french fries ever, throw unpeeled spuds in duck fat. totally worth the cancer and cholesterol. only way i got a squeamish american friend to try them out was to hide that detail from him.
i may be a picky eater, but i will try everything at least once, so long as it's not shellfish (allergies). gator tasted foul, but i'm still waiting for the opportunity to try snake and turtle.