L.T.
I always thought it was fun to see people dressed as related people or items like Peter Pan and Tinkerbell, a bottle of wine and a corkscrew, or as each other.
One year, 4 friends each dressed as a Scrabble tile (E, I, L, V). Others had fun rearranging them to spell words. If you like that idea, you could decorate a shirt to look like part of a Scrabble board. Attach a velcro strip along one row of squares. Cut out several squares from felt or posterboard and write a letter on each. Attach velcro to the backs so they adhere to the shirt but can be rearragned.
Have fun!