Paris Hilton calls ex-pal Britney Spears "Animal."

Paris Hilton and Britney Spears are on the rocks, and it looks like Spears, 25, was the heartbreaker reports US magazine.

Weeks ago, “Britney called Paris and said she had decided not to be seen in public with her ‘for now,’� a Hilton source tells Us.

Things went bad after Spears took heat in the media for partying without panties while leaving her two kids, Sean, 15 months, and Jayden, 3 months, at home.

“Britney told Paris that it’s not personal,� says an insider.

According to another source, the heiress, 25, didn't invite Spears to her December 18 Christmas party and now refers to her ex-pal as “Animal.�

“Britney doesn't think about things before she does them. She just acts out,� says the source.

A rep for Paris Hilton told Page Six , "I've never heard Paris use that phrase about anybody, and I won't be surprised to see them together in the future."

Meanwhile, Spears’ soon-to-be ex, Kevin Federline, 28, has been keeping a low profile.

On December 21, he stopped at Target in L.A.’s Woodland Hills area. “He was trying to be cool, dressed in a puffy white jacket and cargo pants,� says a witness to US Weekly. “He looked like he was waiting to be noticed.�

“Someone said loudly, ‘My, how the mighty have fallen – shopping at Target these days?’�