Sulfer hexoflouride
I just saw this video on youtube crazy shit, I wonder if its bad for you??
http://www.youtube.com/watch?v=d-XbjFn3aqE
It actually is harmful in a way but not too seriously
Sulfur hexafluoride is heavier than air and it may get trapped in the lungs.Prolonged use would be more harmful than taking the occassional hit and it should generally have a mix of oxygen so it will be easier to breathe out of the lungs