Big Heads: While serving or during gameplay, press and hold the Left trigger, then press B, A, B, Y for some bighead action!
Big Boobs: It is what it is, folks. During gameplay or while serving, press and hold the left trigger then press B, UP, UP, B, Y. Doesn't work on the guys in the game I hear, but who wants to see a guy with huge hooters anyway?
(Note: you can reenter the codes to reverse the effects)