I know it as "hippy crack." First heard about it when a friend went to the Tibetan Freedom Festival in the summer of '98, took his first hit, and crumbled to the ground as he lost total control of his body. Classic.
You have probably done it....under it's more appealing moniker, laughing gas. A dentist used it to perform my wisdom tooth extraction, that's typically people's first, and only, experience. Well, not in Vietnam.
Drugs suck in SE Asia, apparently. So it's alcohol and hippy crack. I thought the bar I was at was giving out balloons full of helium, for shits and giggles. NOPE! From hostels, to bars, clubs and street vendors, wherever nightlife exists from Hanoi to Ho Chi Minh you'll find foreigners and locals alike, hyperventilating themselves with balloons full of nitrous oxide. Essentially, shutting off parts of your conscious brain to your body, producing a short 10-20 second euphoric, at times giggly, high. I legit watched a girl sit at a bar for 30 minutes with a constant stream of ballon + nitrous to her mouth.
If you're wondering, it's kinda terrible for you. Not as bad as the real crack, or say binge drinking, but first timers can definitely pass out and bust their heads open, as some gringos found out in Hanoi my first week. Classic.