It's possible that you are thinking of a similar idiom, such as:
* "Have a screw loose": This means someone is eccentric, odd, or perhaps a little crazy.
* "Not the sharpest tool in the shed": This is a humorous way of saying someone is not very intelligent.
* "Have a few marbles missing": Similar to "have a screw loose", implying someone is not very bright.
If you can provide more context or the full phrase you heard, I might be able to give you a more precise answer.