At the community bike shop where I volunteer, I have seen University of Delaware students come in with bikes (typically low end MTBs) in amazing states of disrepair. One student was riding a bike where the handlebar had slipped loose from the stem clamp. He was riding it by sort of holding the bar in the clamp area. Yes, it was freely rotating.

Rusty chains are the norm and a significant percentage of the students don't shift the derailleurs.