A mishearing of chickenpox (varicella), a viral illness characterized by a very itchy red rash. Commonly heard in South Wales, in particular Llanelli.
Despite the lipsmackin' monicker, the discarded scabs are NOT recommended for human consumption.
Korean Clerk: What'chu want on it
Me: Salt, peppa. ketchup
Korean Clerk: You want largey "alf and alf"
Korean Clerk: Six dala