The Forgetting Sarah Marshall star, who filed for divorce from the Firework singer in late December, was performing a show at the Borgata Casino in Atlantic City as part of a live tour.
But his set was continually interrupted by a member of the audience shouting out "Katy Perry", and Brand decided to take revenge on the assailant by turning the spotlight on the male and hurling a number of disparaging remarks at him.
Halting his comedy show, he said: "I wanna see what this person looks like. Turn the lights on for me because I want to achieve some sort of confirmation. Who's the person who keeps shouting that? Come here, let's see ya (sic)."
As other members of the audience pointed the suspect out, he added: "Let's see how your mental illness looks in the daylight. It's you, is it? Oh dear.
"I was hoping that your personality was as a result of physical beauty, then I saw you. I thought this guy's confident probably because he's incredibly pretty, but look at you. You look like someone that's fallen off the outside of a church! And what is it that you have rattling inside of your mind? Some bizarre combination of alcohol and idiocy... and yet the confidence to continue shouting!"
Brand continued to reprimand the rude fan and an eyewitness tells Life & Style magazine: "He went on to attack everything from how good he thought the guy would be in bed to accusing him of being impotent. It must have been humiliating for the guy; it seemed to go on forever.
"Eventually he pulled it together and got back on the stage, and being Russell, he told the guy he’d just torn apart that he loved him."