The two were "very cozy with each other ... and very, very comfortable," says an onlooker


If Jennifer Aniston and Vince Vaughn want people to believe they’re nothing more than good friends, they’re going to have to stop acting like this: After mingling, dancing and scarfing down hors d’oeuvres with roughly 200 guests at the wrap party for their film The Break Up – held at Chicago’s hip Bella Lounge Aug. 24 – the two made their way to a private booth and, as one onlooker tells PEOPLE in its latest issue, “got very cozy with each other. Very friendly and very, very comfortable with each other. The hand on the leg, the arm on the shoulder.”

They left at 10:30 p.m. – she in a black SUV, he in a cab – and hooked up with more than 30 guests at a Dwight Yoakam concert at the House of Blues. The New York Daily News reported that the pair “had their arms around each other. Then they were dancing. Then they were straight making out.”

And then it was back to the Bella Lounge at about 1 a.m. with a smaller posse – about a dozen crew members and film execs – for a last round of drinks and a little more conversation. At 4 a.m. Aniston, 36, and Vaughn, 35, left in the same car.

So … friends, or more than friends? “Do not read into this,” advises Aniston’s rep. “At the wrap party … everyone was enjoying themselves, cast and crew included, and they were all being very affectionate to each other.”

Whatever their relationship, it will soon be long distance. Aniston flew home to L.A. the next day – missing by hours the Aug. 25 arrest of a 48-year-old man who allegedly broke into her Malibu pad and told an employee, “I’m looking for Jennifer.” (He remains in custody in lieu of $70,000 bail.)

Vaughn, meanwhile, begins a nationwide comedy tour Sept. 12.