One who eats bad food like candy, frozen pizzas, otter pops, pop tarts, and so on and doesn't eat any healthy food. Reflects that of a college diet. The person does not even need to be fat to be a fatty cakes, they can be skinny and eat a whole lot of crappy food.
Also refers to a Donut.
Yo hommie you are such a fricken fatty cakes put down the swedish fish and cheese cake. Fricken Fatty cakes.