Nick Young's GF -- BOOTY SLAPPIN' ... with Jennifer Lopez

Los Angeles Lakers star Nick Young is a huge friend of his GF's ass ... and so is Jennifer Lopez ... 'cause J.Lo and Iggy Azalea are twerking ALL OVER EACH OTHER in a new video that just hit the 'net.

Lopez just released her new video for "Booty ft. Iggy Azalea" ... and really it's just an excuse for the two badonkalicious women to show off their backsides.

There's booty shakin ... booty slappin' ... booty twerkin ... booty on booty action.

It's insane.