Except for brain-damage and the potential for asphyxiation, you mean?
What, like if you walk into an air-tight Helium-only chamber and lock yourself in? I'm talking about inhaling from a party balloon, that kind of thing. Unless you hang yourself upside-down, you're not in any danger from that.
You can also die from drinking too much water, but it's still fair to say that 'drinking water is totally harmless, even for little kids', because nobody in their right mind interprets that to mean 'drink many litres of water all at once'.
Inhaling 'natural air' can also be fatal if you inhale it through a high-pressure tube forced down your wind pipe and you're otherwise exposed to the vacuum of space.