This one was personally embarrassing. In a crowded line at the Mongolian Grille with a friend a few weeks ago while we were waiting in front of the pasta bar:
Me: So, you going to get your noodle on tonight?
(guy in front of us almost cracks up)
Me: Oh. I've just added another item to my "things never to say in line" list.
This one I'm actually kind of happy about. Earlier today while outside the Alamo Drafthouse South Lamar with friends:
Me: I feel like pulling in oxygen and expelling some carbon dioxide. Oh wait, that's what we do.
enkigrl: What are you today, animal or vegetable?
Me: Actually, I'm mineral. Everyone takes me for granite.