be off (one's) chump

To be crazy. In the UK, "chump" is a slang term for "head." Primarily heard in UK. You're off your chump if you think that plan will work.

Name	Pronounced	Usage
Anri	-	Georgian
Nemesis	NEM-ə-sis (English)	Greek Mythology
Tjaard	TYAH:RT (Dutch)	Frisian, Dutch
Oluwakanyinsola	-	Western African, Yoruba
Koray	-	Turkish
EulÀLia	-	Catalan