The classic is the bowl cut - hair above the ears is left untouched, hair below the ears is badly shaved down to about number 2. Ths should ideally be lopsided with a meander at the back of the head for maximum "specialness".
nb. it is a mortal sin to pull this prank on a woman due partly to the fact that all women everywhere will feel such sympathy for her that you will never get laid again, but mostly because women should never, ever have short hair.
Dude 2: *Laughs uncontrollably*
Dude 1: (touching head) What? Huh? Why's my head shaved? Where's the mirr... A FUCKING SPECIAL NEEDS HAIRCUT??