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
Rahmİ	-	Turkish
Davorka	-	Croatian, Serbian
Leila	LAY-lə (English), LEE-lə (English), LIE-lə (English)	Arabic, Persian, English, Georgian
Michelyne	-	English (Rare)
Bridget	BRIJ-ət (English)	Irish, English, Irish Mythology
Dorris	DAWR-is	English