#2: No good reason: Paul London
When Vince McMahon lost both his hair and the ECW World title to Bobby Lashley in mid-2007, the Chairman of the Board lost a lot more than that.
Seemingly losing his mind, McMahon would act out of character and in his most bizarre moment, walked in a trance to his limousine, which promptly exploded. Not only did the segment (briefly) kill off McMahon, but it (permanently) killed off Paul London, who appeared briefly during the walk.
As one of several WWE Superstars who stood there whilst McMahon walked, London had a big grin on his face, which folks backstage saw as unprofessional of London, who acted like a goof during the sombre moment.
Releasing London quickly after, the talented and popular London probably shouldn't have had his entire career cut short on a grin.