Well, I've often felt like I don't really fit in anywhere. It's much easier to explain my username with an example, so here goes. A machinegun in Ancient Rome would be an anachronism; it's something - person, artefact, whatever - that's out of place, usually in the wrong time period.
That's not to say I feel like I'm living in the wrong time period (that would be crazy), but I do frequently feel like I'm very out of place. Like I said, I don't fit in; I always feel slightly isolated, even from my best friends.