It looks like there's a feud brewing between former best friends Miley Cyrus and Demi Lovato. We're not sure what ignited their fight, but it caused Miley to unfollow Demi on Twitter. As soon as Demi realized what Miley did, she unfollowed the "Wrecking Ball" singer and tweeted a photo of her sold-out arena with the caption, "Ain't nobody got time fo dat!!! #pettybulls— #toobusykillingit #cutethough #NEONLIGHTSTOUR."

Unfortunately, Demi and Miley aren't the only stars who are fighting. Click through to see the biggest celebrity beefs of all time, then let us know in the comments below whose side you'd take in each of the feuds. What do you think happened between Miley and Demi?