I think a good one from evopsych (I got it from Robert Wright's The Moral Animal and maybe also here) is:

"Poorer women try to have children until they get at least one boy, while wealthier women try to have at least one girl." (Truth: it's the opposite -- status helps the reproductive chances of men more than women.)

I like it because it's easier for someone just encountering it to rationalize the false result on the grounds that "Poorer families need hard workers, so they need boys."