Chuck Liddell now realizes the video he made to congratulate a man for coming out of the closet after 40 years was most likely a homophobic prank ... and the UFC legend is really upset about it.
Here's the backstory ... Chuck is one of the celebrities who works with Cameo, a company where people can pay celebs to make custom video messages for fans.
Someone named L-Dogg asked Chuck to make a video congratulating "Timmy" for going public with his sexuality ... and Chuck, believing it was a legitimate request, obliged.
The original video features Chuck delivering a heartfelt message to Timmy -- and saying he wishes Timmy would have been able to come out earlier in life.
But, now it seems pretty obvious L-Dogg was just using Chuck as part of a homophobic joke.
"If this is someone messing with somebody, that's messed up," Liddell told us at LAX.
"I assumed it was a guy who was actually coming out after 40 years."
Bottom line ... Chuck says he doesn't want to be used to make jokes in bad taste.
But, hey, if it wasn't a joke and L-Dogg was being sincere ... CONGRATS TO TIMMY!!!