Don't mess with former UFC heavyweight champs.
Randy Orton found out the hard way at Summerslam over a year ago when he copped an elbow to the head from Brock Lesnar, busting him open.
Last night? It was Braun Strowman's turn.
Strowman - who was wrestling Lesnar and Kane in a triple threat match for Lesnar's WWE Universal Title at yesterday's Royal Rumble - was helping Lesnar up when he went for a knee and messed it up.
Strowman accidentally collected Lesnar in the head with his knee, who wasn't too thrilled about that.
His response? You clock me in the head, I'll clock you back.
Lesnar got up and delivered a legitimate punch to the side of Strowman's head, leaving the big man staggered.
Censored audio apparently reveals Lesnar yelling at Strowman to "slow the f**k down".
Thankfully Strowman seemed to shake it off and the three men finished the match in style, with Lesnar retaining his Universal Title by pinning Kane.