It must be hard to be Chris Brown's girlfriend, what with his hard-partying ways and the need to keep a stack of restraining orders at the ready. Aspiring model Karrueche Tran has made a go of it anyway -- but she was none too pleased to see her man and his ex Rihanna making physical contact of the non-911-variety at the VMAs last week.

A source told Us Weekly that Tran didn't even know Brown was going to the awards show, and that combined with the congratulatory kiss he gave RiRi for winning Video of the Year left her "totally pissed off."

There's been bad blood between Tran and the 'Umbrella' singer for a long time, and for a while they even aired the war on Twitter, so the insider says Tran "felt the kiss was a public slap in the face." Which, we have to say, is better than Brown's usual habit of a private punch in the mouth.

But, go figure, Brown hasn't exactly been respectful of Tran during their nearly year-long relationship. "[She] and Rihanna really hate one another and Chris ultimately just does what he wants," the Us source said. "Seeing him with Rihanna at such a public event made her very angry."

So angry, in fact, that Tran posted an image to Instagram reading, "Treat your girl right."

Good luck with that, lady. You're gonna need it.

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