barmy on the crumpet

Eccentric or weird. In this phrase, a "crumpet" (a muffinlike pastry) is synonymous with one's head, and "barmy" means "yeasty." What do you think of John's strange behavior lately? I'm starting to wonder if he's a bit barmy on the crumpet. He says he's going to start a business selling bees as pets. I think he's barmy on the crumpet. Anyone who would go out in a blizzard like this is barmy on the crumpet.