We have done door decorating just for the fun of doing it. We have done everything from making full door covers with different scenes. We have put our faces into ships and made ourselves look like we were being buried in the sand with just our heads sticking out.
An easy idea is to just buy the stickees, I got mine at Staples, and put them on the door. I got all fish and arranged them nicely. People would go by the room and re-arrange them into other positions. One night, a friend moved them next store to their door.....I came back late that night and seeing them, just tried getting into that cabin!!! Could not understand why my key would not work........while everyone else was inside laughing. It was pretty funny......hehehe