It's happened a couple of times so I understand what you're talking about. It's one of those "once it's been seen it cant be unseen" things. To be honest I think that it's just our over active brains fooling around, with the violent aspect originating as an expression of our own inner discontent. It's like when you hear a joke that is just so inappropriate that it becomes funny. Are you a psycho? No. Just think of it as a twisted sense of humour :P