S. Korea sends out squads to bust kids for...studying...

[Kai]

Could be, though like CO poisoning, with NO it's very possible that you don't realize you're suffocating until it's too late to do anything, like having enough strength or coordination to open up a window. Especially if you're expecting a "high".

I do wonder whether one canister of NO is enough to fill a car.

And I'm not sure, but if you run the AC on internal circulation, there shouldn't be too much oxygen coming from outside in, right? Plus the entire point of NO is that it drives out oxygen.

Which now makes me wonder why don't people get lightheaded from running the AC that way on a long ride with a lot of people in the car?

This is why you're supposed to set the AC system on intake after the car is cooled down with internal circulation. Most car manuals recommend this, I know mine does.