So yeah, it may seem odd to suggest you go out and bash around on a dirt bike to learn how to ride on the street better, but my personal opinion is it's the best thing you could possibly do. Don't feel like taking a class? Get some good gear, and go out looking for ways to crash.

The very first return on the Google was this: http://www.eaglerider.com/dirt-bike-rentals.aspx

About $100/day, and you can rent gear too. You and your buddies go out and act stupid all day long... what could be more fun?

Or, build one of these: