Demi Lovato -- Disses Justin Bieber at 'X Factor' Auditions

Demi Lovato used her "X Factor" pulpit to take not one, but two shots at Justin Bieber during auditions this week ... and there was no mistaking her intentions ... she's no fan of Biebs.

It all went down Wednesday on the campus of USC when Demi took exception to the attitude one contestant was giving off. Sources on set say when it was Demi's turn to give her opinion on the 22-year-old wannabe, she said that the industry already has too many artists with bad attitudes and then commented, "We don't need another little punk running the streets."

Lovato's next shot was less subtle ... when a young man auditioned with Bieber’s own song, “As Long As You Love Me.” We're told the audience loved his performance and so did the judges, but during her critique, Demi remarked, "Well finally someone can sing the song the way it was meant to be sung.”