My 3-year old DS has recently started hitting himself when he is mad or frustrated with something. He shakes his head back and forth and smacks himself in the head repeatedly. I have pretty much ignored the hitting and generally try to calm him down and encourage him to express his frustrations verbally when he gets upset but it honestly really bothers me when he does this. Any thoughts? Should I be trying to get him to stop or just continue with the ignoring and hope the behavior disappears?