True story:
A first officer was eating a jar of kimchi with a fork for that flight's meal (you thought it was a side dish? nope, it's a meal for some...).
As time passed, the pungent aroma of fermented cabbage lingered but soon morphed into a much more threatening beast: the exhaust expunged after the body processed an entire jar of the stuff.
The cloud was filling the cockpit of this jet that already would send used forward lavatory air into the flight deck, let alone let the chamber be filled with the farts of someone who just ate an entire glass jar full of kimchi.
Despite his efforts of blasting the gasper vent directly into his face, the captain eventually became overwhelmed by the relentless, noxious gas and reached for his oxygen mask.
O2 mask inop!
At this airline, there was no requirement to physically remove the mask and check it during preflight, and although the oxygen test function was operative during preflight, it became obvious that this O2 mask was not capable of supplying any oxygen at all once it was removed from storage, nor was the jumpseat mask in a good position to be used as an alternative.
With two hours of flight time remaining, the PIC conferred with dispatch and they made a joint decision to divert to a somewhat nearby airport that would likely have maintenance available to fix the mask.
I'd imagine the mask was officially discovered to be broken upon putting it on for the in-flight lav break, of course.
And no, it was not me, I don't like spicy stuff and I wasn't the PIC either...but this happened just as described above; I know them both well.
