UFC's Daniel Cormier -- Brutal Pie Justice ... Crushes TMZ Staffer

What happens when you call Daniel Cormier the wrong name?

HE PUNISHES YOU WITH A PIE TO THE FACE!!!

That's what happened to this TMZ staffer when he accidentally (stupidly) referred to D.C. as "Jon" during a recent segment on the "TMZ Sports" TV show.

Friday was his day of reckoning ... delivered by Cormier's right hand.