When I worked in a service station, I saw many things.
One day a woman poured water into the crankcase, then was confused to see oil floating to the top. So she asked what oil was doing in her radiator, and we fixed it. Engine didn't run on the mix.
Another guy put 12 litres of oil into his Mitsubishi 4cyl. I tried to stop him, but the customer DOES know best, as he forcefully pointed out before driving off in a clattering, smoking heap.
A guy who put a butane lighter end on under the handle of the petrol pump so the it would keep filling while he went wee-wee.
A guy who blew up two bike tyres by running the air hose flat out.
Another guy who came in with a car looking like a matchbox car (no flat on the bottom), because he did the same as the aforementioned bike owner.