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
Oddmund	-	Norwegian
TorbjÖRn	-	Swedish
Farah	-	Arabic
Castor	KAS-tər (English)	Greek Mythology (Latinized)
Kouta	ko:-tah	Japanese
Abd Al-Rashid	-	Arabic