The new question from the yc application "Please tell us about the time you (...) most successfully hacked some (non-computer) system to your advantage" filters me out right there, so far I can't think of anything. How about you? I love that kind of stories, and I suppose giving them away now won't hurt the applicants chances?
I can only imagine that my whole live is a kind of hack: I hacked my girl-friends brain so that she actually went out with me. I hacked my own brain so that I managed to learn Computer Science, exercise regularly and eat reasonably healthy. I twisted my CV in the right way to land that job etc. And so on... But I guess that is not quite what YC is looking for... But I mean, people's life are essentially an attempt at optimizing their standing in the system, are they not?
I guess I am also not quite the "real world" systems hacker, because often it seems to entail taking advantage of somebody else? Ever since I read "The Art Of Intrusion", I remember it's lessons in all sorts of situations. Like today I was standing in line for cinema tickets, which were likely to be sold out before my turn. It would have been fun to try something, but not really fair towards the other queuing people. Not that I had a really great idea, but who knows, something might have worked (art of intrusion style, discover name of some employee of the cinema, then call cinema and pretend that person was supposed to reserve some tickets for me - one idea).
That said, I'm having trouble coming up with a good example of what would qualify here -- the best I have so far is when I was a new graduate student at Oxford and dug through the Exam Decrees And Regulations (also known as the "big grey book") to discover what nobody else in the Computing Lab was aware of: That instead of writing a 50 page dissertation at the end of my first year and being examined on it, I could count the fact that I had a paper published in a major journal as equivalent to holding a Master's degree, and thereby transfer from Probationary Research Student status to D.Phil. Student status six months early and with hundreds of hours less work.
I would personally call this "reading the rules and understanding how they work" rather than "hacking the system", but maybe that's what they mean.