a) singlespeeds with no rear brake. sure, the front is the more important one, but come on...especially in the rainy season, you'll want that rear brake...oh, what's that? you say you've bought your bus pass already?

b)brakeless fixed with platform pedals. especially on bikes with big gear ratios.

and i've only seen this once, but a dude riding something like 50x16 with only one pedal riding circles in a lane in front of a budweiser truck.

come on, people...