Why cant I get angry?

Basically, no matter how big or small something is, I can never feel anger. Other people will burst when the slightest of things anger them but me, I always try to push it off aside as if its a type of joke or something. I laugh at the dumbest of things and when people do stuff that a 'normal' person will feel anger towards, I laugh it off as if its some kind of joke.

I have never reached the point where my face alone looks angry. Mabye im too laid back or im just a nice person in general, I dont know. But to never feel anger makes me feel like ive got a problem.