Paris Hilton and Nicole Richie
In one of the most publicized (and confusing) celebrity friendships feuds, Paris Hilton and childhood BFF Nicole Richie fell out in a big way in 2005. Neither of the girls has confirmed what actually happened to cause the rift, though Paris did famously tell reporters: "I will not go into the details of what happened. All I will say is that Nicole knows what she did, and that's all I am ever going to say about it."
It was reported that Nicole showed Paris's sex tape to a group of friends at a house party that year, but it remains just a rumor — and let's not forget that painfully awkward fourth season of The Simple Life, where Paris and Nicole were filmed separately. Nicole did tell Vanity Fair in 2006 that after she got out of rehab, she "just decided I didn't want to be her friend anymore. We're just two completely different people; we don't have that much in common."