A cake eater actually refers to Edina, MN, saying the people in it are so rich they can have their cake and eat it too. It could also refer to rich white suburban kids in general, too. And BTW- Mighty Ducks was filmed in Minnesota, so he's probably literally calling that kid a cake-eater from Edina.
"look at that f*cker driving his brand new BMW out of the school parking lot. what a cake eater"