Chris Brown -- I'm Single Now ... 'F***' Karrueche (VIDEO)

Chris Brown has never been good at breaking up with women ... something he proved again Friday night in L.A. during a concert -- when he formally announced he's single by putting Karrueche on blast.

It all went down at Power 106's annual Cali Christmas ... when halfway through Brown's set the singer asked the crowd if there were any single women in the house.

After a brief pause, you hear Chris say, "I'm single too!" ... he then throws a heaping pile of shade at his now ex-girlfriend, Karrueche Tran, saying, "F*** that b****!"

But he wasn't done ... after the show the singer posted a picture on Instagram -- with THREE Kardashian's on his lap, which frankly sounds impossible.