--breaking down the definitions--
NOOB: a newcomer or novice, esp. an inexperienced user of the Internet or of computers in general.
CAKE: a sweet, baked, breadlike food, made with or without shortening, and usually containing flour, sugar, baking powder or soda, eggs, and liquid flavoring.
EXPLAINATION: although the definition of a "noob" and a "noobcake" (when referring to a person) are virtually the same, the use of "cake" on the end of "noob" reinforces the absurdity of the individual's "newbieness".
"Damn, that guy is a real noobcake."
"Jonathan is the biggest noobcake I have ever met."