It's genuine. It's a Cornish slang expression meaning "crazy, loopy, daft" etc., probably dating back a very long way, referring to the "County Lunatic Asylum" that was opened in Bodmin in 1820. It was being frequently used amongst the school children I taught in Cornwall back in the 1970s. I heard it on "Doc Martin", too - so it must still be in regular use. I'm sure current Cornish Mudcatters will be along to corroborate this.

My favourite Cornish expression: "I'll do that dreckly" (i.e. directly) - the Cornish equivalent of Spanish "manana" !

- jeanie