Nick Cannon thinks there's a double standard in Hollywood when it comes to actors with checkered pasts ... and it favors white guys over black guys.
Cannon quickly snapped back at our guy at LAX Wednesday when he asked Nick about all the hate over teaming up with Chris Brown for a new movie because of CB's history with domestic violence.
"What about Sean Penn?" Nick asked, "They ever hate on his past and the movies he did?"
For the record -- Penn's faced allegations for years that he abused Madonna while they were married in the '80s ... but Madonna claims Penn never struck her. Brown was convicted of felony assault for beating up Rihanna.
Still, Cannon says society wants to make black men look like monsters anytime they can. He also tells us his upcoming movie with Brown -- an indie flick called "She Ball" about a women's street basketball team -- is going to be a must-see.
He gives his ex, Mariah Carey, a vote of confidence for her NYE redemption performance, too.