The X Factor creator was forced to call the police after his golf club-wielding neighbour launched a furious rant.
In a video captured by The Sun, the unnamed man launched a 10-minute tirade in the millionaire's street over parking.
The man screamed that he'd "smash up" luxury cars outside Simon Cowell's house and yelled: "I've had enough of Simon Cowell."
The row began on Tuesday night as Cowell’s chauffeur prepared to take him to a Christmas party in a black Rolls Royce.
Other cars then pulled up outside the home of his neighbour, who stormed out of his £2.5million townhouse in Kensington, West London.
He apparently hurled a barrage of insults towards Cowell’s mansion and also shouted that he'd smash the parked cars up.
GETTY IMAGESPARKING PROBLEMS: The neighbour was allegedly riled up over the outside space
“This bloke was properly furious. He was going crazy”Source
It is claimed Cowell’s alarmed minders called in a security team to deal with the incident.
However, they failed to calm the neighbour.
The Met Police stated no call was made to them, but two passing officers defused the situatuion.
A witness said: "I was gobsmacked. I have never seen anything like it. This bloke was properly furious. He was going crazy.
"He was facing Simon’s house just screaming, 'I have had enough of Simon Cowell! Who does he think he is? I’ll smash all these cars up.'"
The insider continued telling The Sun: "It was scary – he was absolutely ranting while waving a golf club about. He started screaming, 'What is he even famous for?'
"The security men were really surprised and tried to calm him down, but he wasn't having any of it."
GETTYANGRY: Simon Cowell's neighbour was allegedly fuming
ITVALERT: Simon's security were sent to deal with the incident
The row was finally defused when police told the neighbour he could be cautioned.
According to the source, Cowell’s partner Lauren Silverman was ushered into a car by security before Simon himself emerged.
The 58-year-old was seen shrugging off the drama outside his £10 million mansion.
When asked if he was having trouble with his neighbour, he replied: "Just a bit," with a chuckle.
Talking about the incident the next day, the golf club-wielding neighbour blasted Cowell again.
ITVCOMPLAINTS: The neighbour said he's 'fed up' with Cowell
He scathed: "I wrote a sign on my door saying, 'Please do not park in front of my house’ and they still did it.
"But I'm always unhappy with Cowell. I lost my temper last night and I'll do it again – do not park near my frontage. It happens every night."
The neighbour also accused Cowell, who suffered a terrifying break-in two years ago, of attracting crime to the area.
The incident comes just weeks after Cowell was rushed to hospital after falling down his stairs.
Daily Star Online has contacted a representative of Simon for comment.