First, assemble the necessary materials. Watermelon, rum, knife, and demonstrator. Today we have a Belgian demonstrator, so I will do my best to do this post in international english.
Grab the largest, cheapest ($4 USD) knife you have in the dorm room
Stab the watermelon to make a hole in the rind.
Realize the knife is to large to do what you want. Replace with a leatherman knife, and cut a small hole in the rind. Enjoy small piece of watermelon
Realize you need to cut a larger hole in the watermelon, so cut another piece out of the watermelon
Imitate the artwork you are creating.
Open bottle of rum (or vodka or spirit of your choice)
Make sure the bottle is actually open.
Pour the entire bottle of rum into the watermelon. You are allowed to sample the spirit you have chosen to infuse the watermelon with.
Keep going! the whole bottle will fit!
Voila! Let sit for 24 hours. If you have a refridgerator large enough, put it in there. Even better, but it in the freezer. Or, if you don't have room, stash in the closet and infuse all your clothes with the wonderful, boozy aroma of rum.