I can relate to this. Especially a lot of what Rachelinpa and Happy Puppy said. (I am also planning to post in that thread about grudges which is floating around somewhere...) If someone really manages to hurt me, I can end up feeling a lot of anger against them and it can be very prolonged (and damaging to me). People generally have also managed to let me down and disappoint quite a bit of late and this turns into frustration, which can turn into a kind of ongoing anger, particularly if I don't get to talk about it with trusted friends.
I also find that I get angry more easily than I used to about things like bad customer service and landlords being mean (both of which I've experienced plenty of lately!). I kicked a bus the other day when the driver wouldn't open his doors though he hadn't even started pulling away But that type of anger tends to be shortlived in me. It does worry me a bit, though. I have lived in a big stressful city for several years now and that might be a contributing factor.
The funny thing is, a lot of people have such a hard time with the idea of me being angry, because I project a very calm exterior most of the time, that they find it very funny. Then they are surprised when I express anger or frustration even in a very contained, moderate way - and if they are one of the few who is the target of a blowup from me, or hears about it, they are truly shocked, as a rule.
I'm realising that things like grudges and anger may not be something you can entirely eradicate from your life if you are somewhat prone, but you can try to minimize them by practicing better mental habits (ie not dwelling on things more than necessary, talking things out with good friends, etc) and taking care of physical health. I have realised that this is a big challenge for me but working on it is worthwhile because it improves the quality of your life in so many ways. I'm also a Christian so feeling a lot of anger goes against my principles - in that way it's also important for me to work against it. I think it can be particularly difficult for NFs though because we feel things very strongly and we can get stuck in those dreaded mental loops of going over hurtful scenarios over and over again.