It's a new one on me--the choking game, or the fainting game. I came across a blog post by a distraught father whose son died this way. The post didn't explain the choking game very well, but I found an interesting entry on Wikipedia.
Wikipedia references a study from the Centers for Disease Control and Prevention that found that 82 children 6-19 years old died while playing this game between 1995 and 2007.
Those numbers are far too small to show up on any broad assessment of health risks to teens.
But each one of those deaths represents a devastated family, with parents and sibilings who might never entirely recover.