Behold the minibike. I've seen one or two people riding these things around Brooklyn, but apparently they've really taken off in San Francisco. The New York Times had a terrific piece in the weekend Fashion & Style section about these street-illegal teensy rides, which included this observation:

According to riders, part of the thrill is the bikes' proximity to the ground; they are only 16 to 18 inches tall. "You're inches from disaster," said a San Francisco rider named Dan, 22. "It's a spectacularly precarious, awesome feeling." Yet many street riders don't even wear helmets. In San Francisco, a typical rider zipping at a fast clip along Page Street last weekend wore shorts, a T-shirt, a backward ball cap and flip-flops.