Jimmy White was given a warning by referee Ben Williams for sticking the finger up at him during his Northern Ireland Open clash with Luca Brecel.
The shocking row came out of nowhere in the fourth frame when the Whirlwind nominated the brown ball only for Williams to accidentally call 'blue ball'.
After White corrected him, Williams laughed at his mistake only for the legendary player to turn sternly towards him and say: "What's funny about that? What's funny about that?"
The 60-year-old then appeared to raise his hand towards the referee, who then said: "Jimmy I'm giving you a warning."
White replied: "What for?" before Williams explained: "For sticking the finger up at me. If you do anything again, it will be a frame to your opponent."
As it turned out, White lost the frame through snooker reasons as Brecel marched through to round three with a 4-0 victory, aided by earlier breaks of 106, 50 and 59.
In the Eurosport studio, Ronnie O'Sullivan and Alan McManus both had sympathy with White and felt he wouldn't have been in the right frame of mind to have a joke with the referee when in such a bad position in the match.
In the evening, three-time event winner Judd Trump suffered a shock 4-1 defeat to Aaron Hill.
It was an almighty win for the Irishman, whose burgeoning career had already seen him win a final-frame decider against Ronnie O'Sullivan in 2020, at the tender age of 18.
Now 20, he showed poise beyond his years to respond to a Trump century in frame two to go on and lead the match again, following up with a break of 87 to move within one of the third round.
A tight fifth frame saw him miss an early chance to wrap up a sensational win but he was soon back at the table to do just that as Trump suffered a shock defeat.
