moggiee, are you sure it was the pilot of a Hunter?
I recall a serious incident in the Hunter simulator many years ago, when the 'breathing air' had been refilled with nitrogen. The instructor thought that the student was being a bit dull, until he failed to respond to simulated radio calls. They opened the canopy and found him close to death....
Since then I never, ever connected my oxygen mask in any simulator!
Slightly less serious was the occasion, early in the days of Anglo-French aircraft, when some bonehead tried to dismantle a helicopter jack marked 'Gonflé à l'azote...' Just as he was undoing the last part of the thread, there was a bang and the jack parted company from the cylinder at a somewhat rapid pace...
Fortunately, no-one was injured. The Franglais label meant 'charged with nitrogen' - which it undoubtedly proved to have been!