Reading this thread make me realize that this rudeness/self centeredness/lack of courtesy problem isn't limited to the DC metro area. The rudeness/selfishness/"it's all about ME" attitude is the norm here. Maybe it's because I come from Pittsburgh, PA, where kindness and courtesy was the rule, not the exception. At least it was in 1987 when I moved to DC strictly for employment reasons. It probably has changed, since this seems to be a national problem. I miss living in that sort of place, where people seem to care about each other.
I've had so many close calls on the "multi use" trails around here that there are days when I want to give up riding. Forget cycling on the roads, as the drivers are even worse. I have to admit that many of my fellow cyclists are at fault, as they go way too fast for the "traffic," don't warn when passing, run stop signs, cut corners, wear those insipid IPODs, etc. I actually worry more about them than I do the walkers/joggers, some of whom I see as "trail blockers" due to their refusal to get over. Anyway, there are blind corners where I actually start saying Hail Marys to protect me from any kamikazee cyclists who might cut the corner at high speed and run into me (it's almost happened several times). I think the unsafe cyclists cause a bit of "rebellion" in the walkers/joggers who end up hating all cyclists, even those of us with manners. My new tactic that seems to work is that after I warn people that I'm going to pass and they don't move, I get behind them and say "I can't see around you to pass" and I hang there, but only if I truly can't see around them or if there are walkers/joggers in the left lane. If it's clear, I will go around them. Most of the time when I'm behind them waiting for a "safe" passing situation, they get over and some have actually apologized. They don't like someone on a bike trailing them at slow speed. I always thank them for moving over, too. Kindness goes a long way, and sometimes, I'll pass or encounter them later and they will smile & wave.
I've actually had people thank me for warning them that I was going to pass because so many cylists around here won't take the time to do so.