Well, I am a vegetarian and I would never eat meat just to be polite, sorry. But, I would make sure anyone potentially cooking me a meal would know that first. I also check ingredients before assuming anything.

Sometimes beliefs prevent people from partaking in things...but that doesn't mean that people are "rude" if they don't want to. It's rude the way some people go about it, but if you are polite and kind, I see no reason why a refusal is a bad thing.