Chuck Liddell Pissed After Being Used In Apparent Homophobic Prank

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.