Why is it that some people are so slow to anger, while other have explosive temper?

Answer 1

I think it's a matter of control and education, plus perhaps how you were raised. When you see that the explosive temper doesn't get you anywhere, you learn to temper it, so to speak. Stay away from people with tempers, they're dangerous and they can't be fixed unless they want to be helped and work on it hard.

Answer 2

There are both nature and nurture aspects to temperament. Some cultures frown on public displays of anger (ex. Japan) while others find it more acceptable (ex. Italy).
Genetics also come into play. For example, the famous feud between the Hatfields and McCoys has been tied to a genetic disposition for anger/violence in the clans (see refd. article below).

Answer 3

I think about the same as Katherine W.

It's a matter of education, maturity and intelligence.