Grudges

I never understood people that held grudges for ages. If I ever get pissed off at someone, I'll block them for a week and start talk to them again like nothing's happened. Or that depends on how pissed, really...
But I've been talking to a guy that really know how to hold a grudge. We're both sort of hot-headed, short-fused opinionated people that are sort of stubborn.
And we had a fight. A silly little "you are no friend of mine" fight.
OK maybe it was more in the dimensions of "you are no friend of mine, and I will unleash DOOM upon you if I ever see you again!"... Anyway, a week later or so, I tried talking to him. He was still pissed. When I say pissed, I mean "DIE YOU BACKSTABBING BITCH!! ARRGGHHHH!!!"

... It was quite unpleasant to be honest, but I guess that that's how some people handle polite conversation.
When I say polite conversation, I am meaning really polite conversation. Like "How do you do good sir!" etc.
Anyway.
What I can't understand is why people are bothered to be mad so long?
It must drain your energy like a sponge that's squeezed.
And quite frankly, I'd rather be a sponge for a week than to be squeezed and squeezed for over a month etc. Man up, and apologize god damn it!