Getting angry or mad sometimes isn't something we want to do but for some reason we just finding ourselves getting angry at some certain things and then try not to over react at that moment, that is for most people who know how to control their level of anger.
Then they are some set of humans that no matter how hard you try to frustrate them, just so they can react in an angry manner they just find a way of ignoring and not letting whatever it is you do affect them. Unlike most people who would react immediately to every little thing you do. Though as human we all have our way we react to things, either calmly, harshly, rudely and so on.
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For me I would say I fall under the category of people that tolerate for a very long time, I react slowly to things and hardly get angry about things well that is because I have realized that not being able to manage your anger would only may you lose, destroy or find it hard to get some things and people will always find it hard to associate with you. Even when they are the ones that will always want to push you to the edge.
With this there are some people that even if they finally do think of a new way to piss me I still just can't get angry at them for a long time. The first people are my parents, even days that I get angry at my parents because most times they just find a way to always frustrate their kids I can't really just get angry at them for as long as I want not because I can't but probably because to them it shows a sign of disrespectful, so to avoid being seen as a disrespectful child that wasn't given a proper home training I just somehow find a way not to be too angry at them for long.
Then the younger ones, I feel getting mad at a child isn't even a fun thing to do, you might end up beefing them because those set of humans would always get on your nerves and most times they have no idea about it. They will always want to do those things you warned them not to do, to them they are exploring.
Anyways, I don't think staying angry for a long time is a healthy thing to do, we should learn to forgive and let go of our anger and not dwell on it for too long, so no matter how upset people get to us we should always forgive them regardless of who they are.