air duster cans...

some will sell freon in the balloons the same as they will sell nitrous oxide.. this isnt cool!! if you cant see the tank and the tank isnt blue, dont buy it...
this happened more when Chlorodifluoromethane R22 was available, this gas is now banned.. not to say it wasnt just nitrous, nitrous will whip you to the ground also if youre not careful..

http://en.wikipedia.org/wiki/Tony_Thompson_(singer) freon related death..

 

If you really really really feel the need to do stuff like this I recommend using those little cans of e-z cheese (and have a bag of bugles nearby).

 

Yeah I was misled into trying this shit about 3 years ago lol. I was already stoned off my mind for the very first time and my friend suggested getting "duster" (didn't even know what it meant rofl), to lift me up even more. Needless to say it was fun as fuck but when I got home the next day and researched it I was pissed off lol. I felt like a dumb ass for a month.