SLAP-HAPPY BEAUTIES ROIL CLUB: "BAD blood between a Playboy model and an heiress who were recently roommates boiled over into a full-fledged catfight over the weekend.

Playboy model Nicole Lenz, who was rumored to have co-starred with Paris Hilton in a second homemade porn tape, got violent at the Virgin Cola MTV Awards after-party at Exis in Los Angeles when Johnson & Johnson heiress Casey Johnson arrived at the club with pal Bijou Phillips.

Johnson allowed busty brunette Lenz to stay in her house earlier this year and learned to regret it. Johnson and Phillips, who were partying with Nicole Richie and Nicky Hilton, ignored Lenz, infuriating the pinup. According to spywitnesses, Lenz walked up to Phillips and whispered something 'nasty' in her ear.

When Phillips ignored her, Lenz yanked her ponytail and all hell broke loose."