Demi Lovato was left furious following a crass drinking joke on 'The X Factor' USA last night (19.12.13).

The 21-year-old singer, who has battled alcohol and substance addiction in the past, seemingly took offence to a skit that claimed she had been drinking 'annoying juice'.

The star has a playful rivalry with fellow judge Simon Cowell on the singing competition and is often branded ''annoying'' by her British co-star.

The skit featured digitally altered scenes of Demi drinking a green concoction called 'annoying juice', but the joke didn't go down well with the former addict.

While the clip played, Demi was seen turning to her fellow 'X Factor' panellist Kelly Rowland and saying, ''That's f***ed up''.

The 'Heart Attack' singer has been open about her battle with alcohol abuse in the past, as well as her struggles with drugs, self-harming and bulimia.

Demi confirmed this week she will quit 'X Factor' USA after two seasons following last night's third season finale.

She said: ''I started the show being a singer and a musician, and so I'm going to go back to that.

''It's been really great but I'm so excited for 2014. I'm going to dedicate it completely and entirely to music, touring and making a new album.''