Off your rocker

Meaning

You use this to tell someone they are acting crazy or being completely irrational. It implies that their brain has tipped over just like a rocking chair pushed too far.

Playful, skeptical

Used in a sentence

• You want to go skydiving in this weather? You must be off your rocker.
• If you think I am paying that much for a used car, you are off your rocker.
• The boss is off his rocker if he thinks we can finish this project by noon.