Who knew David Arquette and Kelly Osbourne were party pals?

The twosome joined friend Jeff Beacher of Beacher's Madhouse at Yellowtail inside the Bellagio, and we're told the group chowed down on the signature Tuna Pizza. Sounds delish!

After dinner, the group took the party to The Bank Nightclub where they witnessed the "Hottest Baby Momma" contest ... in honor of Mother's Day. Sexy good times in Sin City.

See which Britney Spears' ex was hanging poolside in Vegas over the weekend ... after the jump.