Justin Bieber got into a feeble fracas with fellow party animal David Arquette at his 21st birthday bash as it raged until 7 a.m. Sunday in Las Vegas.

The puny “punch-up” happened after Bieber — who was paid a whopping $500,000 by the Hakkasan Group to host his historic coming of age at their Omnia nightclub — took the party to his “Hangover” suite, the eye-wateringly expensive rooftop villa at the Nobu Hotel at Caesars Palace.

One guest told Page Six that Arquette, Courteney Cox’s ex-husband who has seen the inside of more club bathrooms than Paris Hilton, was “pretty messed up” by the time the afterparty kicked off in the birthday boy’s suite, and was openly “talking about Bieber behind his back.”

The witness said: “Justin heard what David had been saying, and threw him out of his suite with the help of a friend, because they didn’t have security up there. Somehow David managed to get back in and rushed at Bieber to take him out. There was a confrontation, then other people got in the way to separate them. David was thrown out again, this time for good.”

A rep for Bieber declined to comment Monday night, and Arquette’s rep said he couldn’t immediately be reached.

Why cravat-wearing Arquette, 43, was a guest at Bieber’s birthday bash remains a mystery, but he is a partner in Hollywood club Bootsy Bellows with the h.wood Group, which was last year acquired by the Hakkasan Group.

But Arquette’s ego must be pretty bruised after losing out in the birthday bout with Bieber, who famously sparred with man/elf Orlando Bloom over Miranda Kerr last summer.

Perhaps Arquette should have hurled his Bieber insults along with others at Saturday’s Comedy Central roast.

Jeffrey Ross branded Bieber “the King Joffrey of pop,” adding, “Selena Gomez wanted to be here, but she’s dating men now.” Kevin Hart cracked, “Tonight, we are gonna do what parents and the legal system should have done a long time [ago] — give the boy an ass-whuppin’ he deserves.”