Turning down home-cooked meals
This was by far the most popular response. It sucks when someone's gone out of their way to cook, and you're left to awkwardly decline their hospitality.
Being lumped in with snobby vegetarians
This was the second most common response. That person guilting you for enjoying meat? They're the 1%. Most vegetarians hate those types of preachy vegetarians.
Antagonistic, ethical wormholes
If a cow is killed in the woods, and no one is around to hear it moo in pain, will you eat it? If you had to kill a chicken in order to stop a world-destroying plague, would you eat it then? Vegetarians are not excited about answering these types of questions. Most will happily explain their views, if you don't come at them with gloves swinging.