Not one of us is perfect, and all of us are prone to occasionally being inattentive and careless on occasion, and for certain, we all make mistakes.......but that Glock trigger makes it too damn easy to make a mistake of the most serious kind, IMHO.
Nonsense. The Glock's safety mechanisms make truly accidential discharges nearly impossible. Negligent discharges? I think it's pretty much common sense that if one has their finger on the trigger, they can expect the gun to fire, regardless of safety mechanisms in place. As such, one should keep their finger off the trigger and this situation could be avoided.
The only situation where I could concieve of the gun facing upwards would be if one was sitting down on the can and the gun somehow were to face upwards. My experience with answering the call of nature (both standing and sitting) suggests that my pistol will lie horizontally on the floor next to my foot if my pants are around my ankles. I've not been able to get it to point upwards at all.
This goober violated all four rules of gun safety:
Always treat firearms as if they are loaded, not safetied, and ready to fire.
This individual clearly did not treat the firearm as if it were loaded, else he wouldn't have been needlessly handling it.
Always point the muzzle away from anything and everything which you do not intend to fire upon.
Why was he pointing the gun at the ceiling? Why was the gun not in its holster? Shooting the floor would be much cheaper to fix and less dangerous to others than shooting the ceiling.
Always keep your fingers away from the trigger until you are ready to fire.
Clearly not done, as it's effectively impossible to fire a Glock pistol without pulling the trigger.
Always be sure of your target and its surroundings.
Also not done, as he was unsure of what lay beyond the ceiling, or where the bullet would land.
He's exceedingly fortunate that nobody was hurt during the incident, but he's still irresponsible and handled his firearm in a dangerous manner.