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

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

LADY GAGA

When Aguilera returned to the music scene in 2008, her revamped look drew comparisons to a still on-the-rise Gaga. But the "Dirrty" singer denied any similarity and even downplayed her knowledge of the star. "This person was just brought to my attention not too long ago. I'm not quite sure who this person is, to be honest," she told the Los Angeles Times. "I don’t know if it is a man or a woman." Two years later, Aguilera changed her tune, saying she is a fan of Gaga. "I think she is great," she wrote on her website, "and I appreciate any woman fearless enough to go against the norm."