Here is what I'm curious about tho, where were the security guards and metal detectors? The security guards could have noticed that something was wrong and removed him before he had the opportunity to shoot and murder Christina. Also, at all of the concerts I've been to there has always been metal detectors to make sure nobody brought weapons into the venue. Where were the metal detectors at that concert?
In all serious, nobody knows when their last day on this world will be so we should be respectful to everyone we meet and treat them like we would like to be treated. Everyone has bad days;that's a part of life; but a smile goes a long way or just simply a "Hello, how are you today?" People will take that and then spread it to more people they encountered throughout their day. Another idea, is when you see someone having a bad day on Facebook, write a post on their wall(or text them) and them them why you love having them in your life. You could even write posts on your friends' or family members' walls just whenever you feel like it and tell them why you love them.