I fly fairly frequently even though I do not enjoy flying commercial. I have never seen anything close to any of this stuff. I wonder how many people here have personally witnessed crap like this?
About the worst I have seen is people getting drunk and talking loud. Or slobs who do not know how to dress themselves. And the general small annoyances of people who do now know how to act or are just inconsiderate -- bringing on too much carry on luggage, trying to rush to front of plane at landing for no reason like a tight connection, bringing smelly food aboard, bring too fat to fly, poor personal hygiene, using a wheel chair to board for priority but not needing one to deplane (SWA), etc.
The worst thing I experienced was a few years ago I was sitting in First Class and a Chinese national spent the whole flight spitting saliva into a clear plastic cup. Not as bad as snuff. But disgusting.