Whose Side Are You On? Christina Aguilera vs. ...

From The Wanted to Kelly Osbourne, see who's hit a sour note with the singer

ADAM LEVINE

The ongoing rivalry between The Voice's passionate pop stars extends beyond the show. When the Maroon 5 frontman announced plans to launch his first fragrance, Aguilera took him to task on Twitter, linking to one of his prior Tweets that asked for a ban on celebrity scents. "Haha @AdamLevine," the singer wrote. "What a difference a year makes ..."