When it comes to driving, I expect the same courtesies... blinkers equal that very easy "Please" in life and that nice little hand wave equals "Thank You."
Taking a cookie off of my plate, taking a bite out of it and then saying, "Please, may I have one of your cookies?" counts as neither a please nor a thank you. Likewise, cutting me off and then putting on your blinker will not make me a happy camper.
If I go out of my way to help you and you don't say "thank you," I'm likely to resent you and not be as willing to help you the next time (depending on the circumstances). Likewise, if I go out of my way to let you know that I've made room for you in my lane so that you can get out from behind that stopped bus in your lane since you've so dutifully had your blinker on for 500 feet, and you don't give me that little polite hand wave, I'm not going to appreciate you.
I've been driving (as opposed to metro-ing) to work for nearly a month now (since I returned after the kidney stone), and I've amassed a large number of stories about the lousy DC drivers out there. In reality, I much prefer driving to taking the metro, but I just don't understand the sense of entitlement that most people drive with.
Here endeth my rant, for the time being.