In the NFL? I don’t think the palpably unfair penalty has ever been called during an NFL game.
For college football, there may be more recent examples, but a personal favorite involves my Rice Owls awarded a touchdown when a player came off the Alabama Bench during '54 Cotton Bowl to tackle a Rice player. He thought they would only get a 5 yard interference penalty from the spot of the tackle but the refs called for a palpably unfair act instead.
This was back in the days when the idea of Rice beating Alabama would not cause immediate and uncontrollable laughter.
