You prefer climbing over people and/or being climbed over? I like assigned seats, too, but they make me time anxious.

I've never once felt obligated to get on the plane earlier just because I had a window. The person on the aisle knows someone will be getting into the empty seats, so they leave their seatbelt undone and get up when I arrive. I do the same if I have the aisle. Maybe this makes me an asshole, but I don't think this is one of those "common courtesy" things; after all, airlines are far from standard in boarding process; I don't think boarding groups usually favor window first; if anything they're random or start from the back of the plane first, or something like that.

I wouldn't worry about it so much if you can help it; I think it's just normal to have to get in to a window seat. If it bothers you, perhaps select the aisle and comfort yourself that you're being nice by boarding last :)

I used to wait to be the very last person to board the plane. I saw no reason to board early and then wait around while everyone else boards. Unfortunately the recent move to charge for checked baggage has made that approach problematic because far more people are bringing full sized carryons, making overhead space precious. However if you have minimal carryons, I'd recommend being the very last person to board--it is far less stressful.

These days, I just don't fly unless I absolutely have to.