Demi Lovato's co-hosting stint at the Teen Choice Awards on Sunday (22Jul12) got off to a critical start as her X Factor boss Simon Cowell warned Glee actor Kevin Mchale about the star standing next to him.

After complimentary comments came in via satellite from fellow judges Britney Spears and Antonio 'L.A.' Reid, Cowell got critical in a video message beamed onto a large screen above the singer/actress right at the top of the show.

He said, "I need to speak to you Kevin about your co-host, Demi Lovato. I've been working with her for the past few weeks and she is annoying, obnoxious, disruptive, gobby, irritating, bad manners (sic), not great taste... she's a brat, I could go on for hours."

But then he added, "That's what makes her special and I really do love her, a bit. Have a great night. Wish I was there but no one invited me."

Lovato fired back, "He's just old... He isn't used to women in this century being able to sit with him."

The joking follows weeks of speculation suggesting Lovato has developed a crush on her boss.

The Skyscraper singer brushed the rumors aside during a recent radio interview, stating, "He's a nice looking fellow and I know that the older ladies love him, but he's not my type."

There was also a flashback for McHale at the top of the awards show as Lovato introduced footage from a video featuring his former boy band NLT.

There was more humiliation for the Glee star as his co-host forced him to audition for her.