The judge was left visibly annoyed after he and David Walliams were enlisted to perform as ventriloquist dummies as part of Jimmy Tamley’s semi-final performance.
Both Simon and David were wearing mouth masks as Jimmy made a series of jokes, mostly at the music mogul’s expense.
He then called for the pair to perform a can-can, but while David was more than up for it, Simon was somewhat less keen.
As an embarrassed Simon refused to rise from his chair, Jimmy pulled at his legs to get him moving - which worked, but it sent Simon walking off the stage rather than getting him to jig about.
Jimmy was quite obviously unsure what to do next with his act, left trying to fill.
Eventually, Simon reappeared on stage having taken his mask off, before the performance then ended with him and David being shut in a large crate, for reasons we’re not entirely sure of.
As the judges gave their feedback, Simon remarked: “When the credits roll up later on, you’re going to see the names of the people who produce this show. When you read about them being murdered in two days time, I’m going to admit, I’m the person [responsible].”
Jimmy replied: “I’ve never had anyone walk off before.”
In the ad break, David later tweeted: “I think @SimonCowell is traumatised for life.”
The Britain’s Got Talent live shows continue on Friday at 7.30pm on ITV.