When Cameron Diaz hit up a post-Golden Globes bash at Sunset Tower on January 15, the Bad Teacher was overheard telling pals, "I have the best ass for someone who's 39!"

Her on-and-off hookup since 2008, Sean "Diddy" Combs, certainly thinks so. An eyewitness tells the new issue of Us Weekly (on stands Friday) that just two days prior, Diaz "was straddling him" at the booze-filled CAA gala at Soho House in West Hollywood.

"Her hair was all crazy, her makeup was smeared and they made out in front of everyone," the eyewitness says. "She was acting like a teenager!" (Diaz's rep denies the makeout.)

Find out more about the two stars' PDA in this week's Hot Stuff video, as explained by Us' Senior Editor Ian Drew and Bravo star Tabatha Coffey.

Also in the roundup: Angelina Jolie snubs George Clooney's girlfriend Stacy Keibler, Michelle Williams dreams of Heath Ledger, and much more!

Watch Us Weekly's Hot Stuff video now. Plus, check out new episodes of Tabatha Takes Over Tuesdays at 10 p.m. EST on Bravo.