Thing that pisses me off: Being a nice person and getting taken advantage of.
Some will say anger is childish and immature. An adult will take a deep breath and move forward, letting go of the anger and move forward constructively.
Fuck that, I say. Anger is a healthy emotion that ought to be expressed. You can't move forward until you've allowed yourself to feel an emotion. For me, doing so frequently requires storming around my house slamming doors, punching stuff, and making a loud noise close to URRRARRRGH!
I also use strong, creative language like fucktard. That's one of my favorites.
But that's in private. With others, I tend to avoid confrontation and then justify doing so by saying I only like to politely address an issue with someone when it threatens to be a long term problem. In that situation, the key is avoiding The Snap. I don't want to retort to a completely oblivious comment with a nasty comment, since that smacks of passive aggressive, another Thing that Pisses Me Off. Luckily, I'm pretty good at doing so. Except, sometimes, when my mother is concerned. My trick is to speak slowly and focus on breathing.
On the other hand, who wants to smile and make nice when inside you're seething. That is being a Phony, another behavior that Pisses Me Off.
What's the balance? Usually I allow space between myself and who's every Pissed Me Off; I need some time to cool down and move forward; no more than a day or so usually. Then my first encounter is typically a little strained, but whatever I liked in the first place about the person who pissed me off generally comes to the surface quickly and the whole thing is water under the bridge.
Not that I forget. People only get so many freebies.