Rihanna, who was signed to Def Jam Records during Reid's tenure at the label, appeared on the Wednesday night episode of the reality show as a guest mentor to Reid's team of aspiring male vocalists, and she confessed the music mogul isn't the easiest person to work with.
She said, "I don't know who's more competitive between L.A. and Simon. They are both very stubborn individuals.
"Simon is very raw - let's put it that way - with the way that he approaches critique. But it's very honest. You have to listen to everything he says, no matter how nasty it might sound.
"I know what it's like to audition for L.A. He can definitely be a pain in the a** as well. I have to say, he will find a way to make you feel you might have a second chance on a nice day but he rarely gives second chances. You have to really impress him in a short time."
But the Bajan star insists the harsh criticism wouldn't have deterred her from pursuing her pop dreams on a TV talent contest like "The X Factor" - if she had not landed her big break when she did.
She added, "Six years ago, before I was signed, if it was "The X Factor" that had come first, I definitely would have entered to have a chance at fulfilling my dream. With this show, it's all so exciting, and it's like a party!"
How do you think Rihanna would have done on "The X Factor"?