Need help on how to make a shirt for school spirit day ! please helpp !?

so im a sophomore and tomorrow is battle of the classes its when all the classes battle eachother in events. anyways sophomores are surfing sophomores ( yeah i know thats pretty gay ) i dont knoe how to decorate the shirt. on the back im gunna have class of 2013 but idk about the front. my colors are black purple and white. i got a white shirt and im gunna cut it so it hangs off my shoulder and wear a bathing suit top under neath . please help me to figure out how to decorate the shirt ! thanks :)