To get the Robot Chicken hat, just sign up for the Adult Swim newsletter by July 4.
In related, not-completely-predictable news, the FAQ for redeeming the Robot Chicken hat asks and answers an intriguing question:
Q. Are you making a Team Fortress cartoon?As long as it's not called "The Hatsure Brothers" or any variation thereof, an Adult Swim Team Fortress 2 cartoon sounds like something we could get behind.
A. Go ask your mother.
In still-related, by-now-old news, Valve launched the "Meet the Pyro" video and announced the Source Filmmaker movie-creating tool today.