Turns out RAY J has another sex tape kicking around.  And this one is with JOAN RIVERS.  Obviously, it's a JOKE.  They did it to hype Joan's We-TV show "Joan & Melissa:  Joan Knows Best?"

In the clip, Ray and Joan are in bed together ... with a video camera.  And Ray tells her, quote, "You're twice the woman Kim was."  And she tells Ray, quote, "Once you go Jew, you know how to screw."

WARNING!!!  It includes some moaning and questionable language