Simon Cowell may be happier on 'X Factor' these days, but his sharp tongue is still in effect. The singing competition judge recently slammed Lady Gaga by calling her "the most boring singer in the world."

Cowell also had the same to say about several other superstars. He told the Mirror, "If you only ever heard Lady Gaga, she’s the most boring singer in the world," adding, "Same with Beyoncé. Or Katy Perry."

This swipe at Gaga doesn't come as too much of a surprise. In August, the producer told Life & Style that the pop star would have been booted in a heartbeat, if she came across his 'American Idol' panel. "She would have been thrown out within 10 seconds,” he told the magazine. “Even if she had walked in with a lobster on her head, it would've been one of the kooky auditions."

Still, Cowell admitted that Gaga does have star power. "You have to be open-minded and embrace that level of expression," he added. “You hope to God you find someone like her."

Cowell is currently the face and executive producer of the US version of 'The X Factor,' which premiered on Sept. 21. He is joined by Paula Abdul, L.A. Reid and Nicole Scherzinger, who round out the judges' panel.