When I communted regularly while stationed in Wash D.C. I used to wear a hockey elbow pad on my left elbow. A quick downward motion will take off the passenger side mirror on most American cars and darn near any rice burnner. I only resorted to that if a guy put his cage in close enough proximity and was being aggressive. For those drivers who absent mindedly "wandered" over into the bike lane, I would just tap the passenger side glass with my padded elbow. Got a few priceless looks over the years with that move. Like they couldn't see the guy in a Day-Glo orange jearsey with reflective chevrons printed on the back.
These days I live in a more commuter friendly environment, but still have to occasionally start a sentence with, "Listen real close you freaking moron...."