Judy kidding

A variation of “just kidding.”
The name Judy comes from Judy Sheindlin, the no-nonsense judge from the American reality tv court show “Judge Judy”
When someone says they are “Judy kidding” they are actually completely serious.

Mikey: You have a booger on your face.
Ricky: Are you serious?
Mikey: Judy kidding.
Ricky: (wipes booger off face) Thanks dawg!