I worked at a restaurant once and a man was extremely intoxicated so we had to ask him to leave. We even offered to get him a cab home, free of charge.
Well, he didn't like that. About 10 minutes after he left the premises, he came storming back in with a large cup of gas station coffee and THREW IT in my managers face calling him every name under the sun...
Luckily, we caught the whole thing on our security cameras.
Craziness!! What's the most unbelievable thing that's happened while you were working?