Just remembered a good one.
I work at night, and have for several years. A while back, a group of us went into an empty office to try to catch sight of an eclipse we'd heard was happening that night. We were all chatting about the eclipse - what, exactly, an eclipse is, etc. One of the women came out with, ". . . because as the earth revolves around the moon, . . ." I almost fell over.
I kept trying to tell her she was mistaken, and that the moon revolves around the earth, which revolves around the sun. She absolutely insisted that I was the one who was wrong. Unfortunately, it was before we had internet at work, so I couldn't prove her wrong as easily as if it happened today.
I think that was probably one of the most frustrating moments I've ever had.