Chris Brown and Karrueche Tran's Run-In At Kylie Jenner's Party

Chris Brown and his ex, Karrueche Tran, both showed up at Kylie Jenner's birthday party, and judging by the look on Karrueche's face ... it will be a looong time before it happens again.

We got video of Chris showing up with Scott Disick and cruising into the party. Everyone seemed happy.

The exit shot ... not so much. Karrueche walked out with girlfriends and when we asked how it was hanging out with Chris -- well ... you really just have to see her facial expression. Kinda says it all.

Karrueche dumped Chris more than a year ago after finding out he'd knocked up Nia Guzman.