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
Kimbrough	['kimbrə]
Dafydd	-	Welsh
Ranulph	-	Scottish
Lyubov	lyoo-BOF (Russian)	Russian, Bulgarian, Ukrainian
Lekan	-	Western African, Yoruba
Naz	-	Turkish