I work in the book trade and I know some dumb questions and statements.
My favorite
I'm after a book but I can't remember the title or author. It's got blue on the cover though.
and
Me: Would you like a bag with that?
Customer: No thanks, I'll save a tree.
Me:
(Thinks about the fact that while bad for land fill a plastic bag is not made from trees.)
You'd be amazed how often I get both of those.