I have a similar story but it's not about astronomy, but anyways, here goes:

I was talking with a friend while having lunch at the University one day and we were talking about hyenas. One girl who was sitting near us said: "what's a hyena...Oh that's like in the Lion King?" (the kids movie). Although I didn’t know who she was I replied: Yeah but the real ones don't speak.

Ouch! Don’t quit your day job!