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Joaquin Phoenix

John Paul Filo/CBS

Joaquin Phoenix made a cameo at a private house party in Brentwood Friday night. The oddball stud, now more famous for his weird rant on David Letterman than working, was at power agent Ari Emanuel's pre-Oscar party.

So how was the once cutie behaving?

"He was completely low-key," is how our inside source at the exclusive to-do puts it. "Joaquin was dressed in a black jacket and happily—for him—made his obligatory social rounds at the party."

We're told the clean-shaven actor looked cute, but slightly bloated as he hung at the house. Whatevs, 'tho we're just happy he's alive!

"[Joaquin] wasn't drinking and looked like he was enjoying himself as he hung out with good friend Casey Affleck."

Uh-huh, suspicious since the funny pair was rumored to be documenting Phoenix's too-weird behavior last year. But then again, if it was all for show JP wouldn't be a Blind Vice all-star, would he?

Another stud outside the party not exactly acting strangely either was...

Justin Timberlake, scruffy and sexy, but sans GF Jessica Biel.

JT who is doing a helluva lot more acting than singing recently was overheard telling guests how excited he is to work with ex-girlfriend Cameron Diaz in their upcoming flick Bad Teacher.

"Timberlake was smiling the entire time he was talking about working with his ex and said Cameron was looking forward to it too," our eavesdropping spy says.

Still, don't take Jess' absence as a sign Justin is read to ditch his now successful babe.

"Jessica was working," a source tells us of her notorious absence throughout the weekend.

What's more puzzling is why Timberlake totally avoided his gal's new bestie...

Jennifer Garner looking toned in black and rather Alias-like accompanied hubby Ben Affleck at the event, and she didn't say hi to JT at all.

Instead Garner was all smiles again as she hung by Ben's side. All good in paradise? Uh, hardly babes.

Affleck was happiest when he was next to...

Matt Damon, who "looked adorable." It's always refreshing to see a Hollywood friendship that lasts!

"Matt and Ben were laughing and smiling the whole night," a source at the party tells us. "Damon, who rarely let go of wife Lucinda's hand, held court next to Ben most of the party."

Other notable guests at the party included: Victoria Beckham, Janet Jackson, Taylor Lautner, Russell Brand, Tyra Banks, Emma Stone, Josh Brolin, Diane Lane, a solo Ryan Phillippe, Quentin Tarantino and Mark Wahlberg

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