Depends on how edgy you want to get. If you want to get so edgy that you have eight people in the audience and no one knows what's going on, by all means, go for Sarah Kane.

 

I also have a play that is edgy and completely inappropriate for schools called The World's Largest Rodent - here's the blurb:

 

"Billy's life was pushed to the brink of insanity when his father disappeared and his mother slipped into a catatonic state after a failed suicide attempt. His older sister, Meg, has enough on her hands with a job at Wal-Mart to pay off medical bills and a Latin lover who is determined to teach Billy how to be a man. Billy's only friends are a home schooled lesbian evangelist named Chastity whom he desperately lusts after and a large, magical talking capybara, the world's largest rodent. Together, they must find a way to revive Billy's mother and save Billy's world."

 

You can read it for free here: