Bobby is Special

From the Publisher's Website:

"Bobby is Special" is a role-playing game about people suffering from mental retardation. It is a game of challenges for the challenged. If you've felt the need to role-play a character who is special, this game is for you.

User Summary:

Players have a set number of dice, equal to their character's level, that is shared between a Tard pool (Retardation; used to perform tasks) and a Spaz pool (Spasmodicity; used to fuel Spaz Attacks). When the player tries to do something and fails, dice move from the Tard pool to the Spaz pool. Whe the character suffers a Spaz Attack, the dice move back into the Tard pool.

For each action resolution, the GM sets a Difficulty (not known to the player in advance, but roughly equal to the mental age required for success). The player chooses how many (six-sided) dice they wish to roll from their Tard pool. Each die lower than the Difficulty move to the Spaz pool. If there are any dice equal to or greater than the Difficulty then the action succeeds.

There are additional rules for handling resisted actions and challenged actions. And, of course, Spaz Attacks.