have bats in the belfry
To be crazy; to act, think, or behave in a foolish or nonsensical manner. Tommy must have bats in the belfry if he thinks he can convince our mother to let him get a tattoo for his birthday. There's an old lady who stands on the corner yelling at strangers all day. I think she might have bats in the belfry.
bats in one's belfry, have
Be crazy or at least very eccentric, as in Sally thought her aunt's belief in ghosts indicated she had bats in her belfry. This term in effect likens the bat's seemingly erratic flight in the dark to ideas flying around in a person's head. [Early 1900s]