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Jack Osbourne vs Aaron Carter
Back in the heydays of their reality show, Ozzy's kid and the younger brother of Backstreet Boy Nick Carter got into it. Jack said Aaron acted like an "irritating little bastard" and he would "gladly kick the s*** out of him." Aaron responded by calling Jack "brain-dead" and "the biggest brat of them all on his show." Hard to argue with either of these points.