She was also a bit of a roastee, as her "X Factor" boss Simon Cowell poked fun at her in a pre-taped video that aired near the opening of the show. The segment teased at the kind of push-pull viewers can expect from Cowell and Lovato when "The X Factor" kicks off in September.
Describing Lovato, Cowell called her "annoying, obnoxious, disruptive, gobby, irritating, bad manners, not great taste — did I say irritating? Yes? Annoying, very annoying. She's a brat. Um, I could go on for hours, but 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 shot back: "He's just old. He isn't used to women in this century being able to say what they want."
Lovato's "X Factor" co-stars L.A. Reid and Britney Spears also sent in taped messages, with a rushed Spears saying, "Congratulations, Demi, on hosting the Teen Choice Awards. Come back to 'X Factor' very soon."
Lovato seemed eager to please throughout the evening, beaming her big smile as frequently as possible. The 19-year-old former "Sonny With a Chance" star went through multiple outfit changes and hairstyles, and at one point rubbed booties with McHale.
"I just want to point out how hot Demi looks," McHale said midway through the show. "Can we give it up for that?"
One segment found Lovato showing off her tattoos, which include a cross on her hand, the word "faith" on her right arm and the words "stay" and "strong" on her wrists.
Later in the night, she was given awards for Choice Female Music Star and Choice Twitter. She also presented Miranda Cosgrove with the Acuvue Inspire Award, an award given to an inspiring teen celebrity who uses her celebrity power to make a difference in the world. Lovato, who won the award last year, called Cosgrove "an advocate for young people and a champion for education."
What did you think of Demi Lovato on the Teen Choice Awards? Let us know in the comments!