An excuse to jap slap somebody.
Offer them a finchley burn, which they will assume is like a chinese burn. When they hold out their arm, thinking it will be relatively painless, punch them in the groin.
Named after the ghetto of Finchley from which it originates.
"Apparently, a finchley burn is nothing more than a punch to the gonads."
"That was one harsh finchley burn!"