Big Sean -- Shreds Ex-Fiancee Naya Rivera On New Track

Big Sean is so damn happy Naya Rivera is out of his life, he rapped about it on his new single ... and the track is pretty vicious.

"I Don't F*** With You" is all about how infrequently Sean thinks about Naya after their nasty break-up ... even though the whole track is about her. So ... irony?

The song was produced by Kanye West -- and in the spirit of a good Yeezy rant -- Sean calls Naya a ho, a bird brain, and lays down the instant classic ... "I just dodged a bullet from a crazy bitch."