Luke had a song on his first solo CD (I GOT SHIT ON MY MIND) dissing the post-Ice Cube NWA called "Fakin' Like Gangstas." The actual rapping was by JT-Money, w/ Luke doing some spoken commentary, and the intro basically called out Eazy, Ren, Yella and Dre (Dre was ripped for the Dee Barnes incident of '91) as punks...
Then on THE CHRONIC, Dre dissed Luke back on "Fuckin' With Dre Day", where he said "Luke's bending over/so Luke's getting fucked." The video for that song featured a Luke lookalike (w/ a gap between his teeth) getting (implied) sodomy. I assume that's what led to "Cowards From Compton."
PEACE!