got a screw loose

(idiom) crazy, not thinking properly

Example Sentence:

Mom: If you think I’m going skydiving, you’ve got a screw loose.
Son: Come on, mom!
Mom: No way!

If Steven thinks he can go out on a date with the most beautiful woman in school, he’s got a screw loose.

Similar idioms:

1. not all there
2. off one’s rocker
3. all hell breaks loose
4. screw off
5. screw around
6. screw around-2