1. Derfcake is the definition given to a birthday cake with 'derf' qualities. Sometime during one's life, they recieve a cake which doesn't quite become the hit that is once thought by the purchaser.
2. Derfcake can also be used in replacement of 'derf', meaning retard.
1. "That's not a cake, it's a derfcake!"
2. "Bob Saget is a smelly derfcake!"