Ronnie O'Sullivan was told to cut out the nonsense after he made a rude gesture during his opening match at the Betfred.com World Championship at the Crucible.
O'Sullivan played sublime snooker at times as he opened up a 7-2 overnight lead against Liang Wenbo. But when he made a miss in the seventh frame, the frustration spilled over into his body language as he flicked a middle finger in the ball's direction.
O'Sullivan was warned about his behaviour by referee Colin Humphries, and has been told a repeat will result in him being docked a frame.
The 34-year-old is hardly a first-time offender though. In 1996 he was fined £30,000 after attacking a tournament official at the World Championship, and just four years ago he quit his UK Championship quarter-final against Stephen Hendry when only 4-1 behind in a first-to-nine match.
Yesterday's offence was not on the same scale as those however and O'Sullivan is unlikely to be worried by the warning.
The opening nine frames of the clash with Liang summed him up, with a touch of the good, the bad, and the ugly.
Centuries in the third and fourth frames, an 86 in the eighth and a 56 in the ninth which could quite easily have become a 147 were the highlights.
He will be less keen to revisit several other frames, however, during which he and the increasingly lax Liang traded blunders.
The man O'Sullivan beat in the 2008 final, Ali Carter, made sure of his place in the second round, defeating Jamie Cope 10-4.
Former poker club croupier Martin Gould shocked World No.8 Marco Fu, winning 10-9.
Mark Williams last night clinched his place in the last 16, as the Welshman beat Scotland's Marcus Campbell 10-5.
Former World champion Steve Davis trails fellow Romford man Mark King 5-4 going into the final session today.