Not Into Elves? Become a Chipmunk
Sucking helium solely for the effect it has on your voice is a time-honored tradition among kids, and probably the only instance of substance abuse you won't get vilified for.
Couple that with an effort like Elf Yourself, and you've got a bonafide interactive promotion for Alvin and the Chipmunks, the feature film based on our favourite childhood show. (Next to Shera and He-Man, anyway.)
Hit Munk Yourself to get "munked," (Get it? Chipmunks?) without the helium. It's definitely safer, even if it cuts the fun in half.