One that is such a douche that if you put cake mix, eggs and batter, and mixed them together. Added a little douche, put it in the oven for 35 minutes. that person would come out of the oven.
A douchebag would be someone like Tiger Woods, Bono or any of the members of Stone Temple Pilot. A Douche Cake would be someone like Mel Gibson, Tom Cruise, Arnold Swarzenegger, or any of the members of Hootie and the Blowfish.
An entity that is so full of the quintessential essence of a douche that if the following recipe were followed:
"Mix 1 part cake mix, 2 eggs, 2 parts and 70 parts douche. Put in the oven for 35 minutes at 500 degrees, stirring halfway."
The previously mentiones entity would be yeilded by the oven.