For me it depends on the situation, for instance, someone butting in line at the grocery store, I'm just gonna laugh and say to him, "Gotta saves those milliseconds where you can eh?" I've had varying reactions to this, some laugh it off, some suddenly realise what they did and apologize, and the rare few get really upset with me for calling them out, those are the fun ones.
I've got far too many stresses in my life to worry about other peoples dickery when it's just a minor inconvenience, but if said dickery directly puts myself or another in harms way, then my fuse is -very- short. For example, when some blonde, barely-got-her-learner's ditz blows a red light because she's too busy talking on her cell phone while I'm crossing with my then pregnant roomate, I lost it, I actually kicked a dent in her rear door as she blew by, which made her pull into a nearby parking lot and then proceed to scream at -me,- which made me scream back, which then attracted an audience, and ten minutes later, the police. no one was injured, but I walked away victorious after -she- got a ticket for blowing the light, which in Canada, means she loses her learners license and has to go through the -whole- process over again.
And finally, there is an exception to my "Minor inconveniences" rule. And that's when I am witness to someone being abusive to a cashier. I think it's simply because I've worked as a cashier for too long, and feel protective of my brothers and sisters of the cash or credit, but if I see someone yelling at a cashier, I get really agitated, to the point I've stepped in to defend the cashier on a number of occassions, and thanks to the fact that I'm just a customer, I get to say all the nasty things I -know- the poor guy or girl behind the counter wants to. I even got a book ten percent off for forcibly marching a disgruntled man out the door, was nice to feel like the brave hero for once, rather than just reading about it.
And wow... this ost got a bit longer than I thought it would...