JEN & VINCE'S FIRST FIGHT!

There are three important firsts in every romantic relationship: the first kiss, the first night together, and the first fight! On Dec. 1, Jen Aniston and Vince Vaughn got to put a check mark next to No. 3 — and it was a doozy, sources tell Star.

The evening at Jen's Hollywood Hills ranch house started out quietly enough, sources tell Star.

Vince, 35, tired from a long day on the set of his new movie, an untitled David O. Russell comedy for which Vince is earning $12 million, showed up looking forward to a relaxing night with Jen, 36.

BAD TRIP
Instead, sources say the conversation drifted into dangerous waters: his Nov. 29 run-in with the law, when they were stopped by police in Scottsdale, Ariz., and Vince blew a .08 on his Breathalyzer test, not quite enough to merit a ticket. The police stop — and the publicity — ruined his vacation, Vince complained.

Then, says the source, "things escalated. Vince blew up with Jen over a lot of stuff: He's sick of being trailed by reporters, he's fed up with Jen's fascination with Brad [Pitt] and Angelina [Jolie] — he even accused Jen of using him as a sex object. He was angry, sweating and raising his voice."