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
Filippa	fee-LIP-pah (Swedish)	Russian, Greek, Swedish, Italian
Stewart	STOO-ərt, STYOO-ərt	English, Scottish
Lanny	LAN-ee	English
Alim	-	Arabic, Uyghur
Edelmiro	-	Spanish
Hiram	['haiərəm]