The last time -- and it will remain the last time if I can help it -- I rode on a commuter-heavy MUP around here, I had had enough.
There were plenty of really bright lights that made it hard for me to see where the hell I was going, but the straw that broke the camel's back was a rider that had at least something like a Dinotte 200 on his helmet and God-knows-what HID on the bars. I was so pissed by this point that, instead of covering my face, I raised my hand and flipped him off, probably getting my finger within a foot of his face.
I KNOW he saw it. That's why I did it. And if he's on this forum -- yup, that was me, and yup, you were a prick.
I shouldn't be surprised, though -- this is DC, after all.