This is something I've thought about writing in my blog many times, but I can never figure out how to say it so it doesn't seem petty. Part of it is being annoyed by selfish people, but part of it reflects my natural ability and propensity for looking at things systemically -- stepping out of my own perspective and thinking about what makes sense for the community as a whole.
The thing that always reminds me of it is when I go to get a glass of water from my office's bottled water dispenser. The office follows the obvious and unspoken rule: if you're the one who takes the last of a bottle, it's your job to switch to a new bottle. And this is a remarkably equitable rule. The odds of you being the one to change a bottle are exactly proportional to how much you use the bottled water compared to everyone else. If Bob uses twice as much water as Jane, today Jane might happen to be the one to hit the bottom of a bottle, but over the long term, Bob should be the one to hit that point exactly twice as much as Jane, and that's perfectly fair.
But suppose that Jane happens to be a selfish moron. In that case, when she hits the bottom of the bottle, she just walks away. Bob gets there to find an empty bottle, and now he has to do Jane's share. He grumbles about the selfish people who won't do their share and force him to do it. So far, what we have is a zero-sum game: for every bit of bad Jane avoids, exactly that same amount of bad gets dumped on Bob.
But now consider the fact that the bottled water dispenser includes a system to heat or cool the water so you don't get lukewarm room temperature water. This only works if there's water in the system, though. Not only does Bob have to suffer doing Jane's share of the bottle swapping, his reward for this is to get stuck with lukewarm water.
For some reason the systemic inefficiency of this offends me almost as much as Jane's root selfishness. Jane isn't just making things worse for Bob, she's also making things worse for the entire system. This is what I find myself thinking: "If Jane is going to be a selfish [word omitted], at least she could do so honestly. She should tell Bob, 'Because I'm selfish I left you to change the bottle. You might as well do it now so you'll at least have cold water later.'"
There are plenty of situations like this. A similar office-related one: I have a few cans of soda in the fridge and a 12-pack of soda next to it; when I take one can I replace it so I always have some cold. When people steal my soda it irks me, but it's less than 25¢. However, finding I don't have a cold soda when I want one makes me fume. Why can't they at least put another can in after stealing one of mine?
If someone steals your wallet, they don't really want the wallet itself, or your library cards. Probably they don't even want your driver's license and social security card. They might even have no interest in your credit cards; many muggers are just out for cash. But are they going to give that stuff back? Unlikely, even in situations where it adds no significant risk for them. So you're out the cash they gained (zero-sum), but you're also out a bunch of time and money to replace all those things. You may well find yourself thinking, who cares about the $50 I was carrying, compared to the day off I'm going to have to spend at the DMV office!
It would be nice if things could be arranged in such a way that the selfish people only stole what they took from us, not something extra robbed from everyone, too.