Blac Chyna -- Sorry Rob, Kim Kardashian's No Psycho Killer ... But She's Still Dead to Me

Kim Kardashian's former BFF Blac Chyna did something shocking by standing up for KK in the family feud with Rob -- even though she's pissed Kim's little sis swooped and scooped her ex.

We got Blac Chyna outside Greystone Manor Sunday night, and asked how she felt about Rob Kardashian comparing his sister to "the bitch from Gone Girl." We fully expected her to pile on ... especially since she and Kim had a falling out when Kylie Jenner started dating Tyga.

You gotta see this clip ... because at first it seems like BC and Kim signed a peace treaty. But when we ask if they're friends again -- the temperature plummets 20 degrees.