Pain induced hypoxia is a good one. That being hypoxia that stems from a decreased minute volume due to pain on inspiration. Namely broken ribs, but I'm sure there's a plethora of conditions that would cause this trouble.
Especially for the BLS guys who might not necessarily have any pharmacological analgesia.
Seeing as you are looking for experience: When I had my appendix out I had a left over bubble of laprosocopy gas left over which was quite painful for a few days, particularly on inspiration. after a few moments I would start to feel increasingly short of breath which would make me breath harder which hurt, etc. It would come and go in "attacks". Whenever I'd have an "attack", they would whack a pulse ox on, and a nasal cannula and 5 mins later, no troubles.
I like the idea of this thread. As time goes on I think we are going to see more precautions and relative contraindications for certain Fi02s. We sit an learn at uni how archaic the "Everyone gets 8 through a hudson" idea is, then we sit down in prac classes and that's exactly what we get taught to do. It grinds my gears.