Kim Kardashian and Paris Hilton. They'd been friends since preschool, and remained so into their 20s, but with the release of Kim's sex tape in 2007, she started eclipsing Paris as America's favorite "celebutante."
Paris apparently wasn't cool with that, and the following year she effectively ended their friendship by saying that Kim's ass looked like, "cottage cheese inside a big trash bag." They made up, but the friendship never really recovered.
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