I have a few
- I worked in a newsagent with a post office when 9/11 happened and we had a customer come in on 12th with a parcel to be sent to NY. She was apoplectic when she was advised that it might take a little longer than normal due to the ongoing situation in NYC,
and insisted on writing to head office to complain!
- This wasn't a job - just a volunteer role in a situation where we were all volunteers. I had made up a rota for everyone involved in a particular role. Prior to making up this rota I had emailed everyone involved asking for any dates over the next 3 months that they couldn't do. I emailed several times and made it clear when I needed to know by as the rota had to be done by a certain date.
When the rota went out I was confronted really aggressively by someone because I had put them on duty on their wedding anniversary 2 months later. I apologised, but explained that I didn't know as neither they nor their spouse had replied to any of my emails, however, as always, they were free to find a swap with someone else on the rota.
This wasn't good enough and I should have phoned everyone personally (there were about 30 people on the rota!) to check before I sent it out! By this point I was really being yelled at in a very aggressive way and someone else stepped in and immediately offered to swap the date thereby solving the problem. This also wasn't good enough because it should never have happened in the first place, etc etc.
This went on for several minutes after which I said that I had done everything I could and I wasn't listening to abuse so I walked away.
It was absolutely horrible.
To make matters worse however, the following week I was asked to meet with this person - I thought they were going to apologise! How wrong I was! They complained that I had no leadership skills and should never have been put in the role I was in because I couldn't take criticism because I had walked away, and I would never amount to anything if I couldn't take anyone telling me I was wrong.
I (once again) tried to explain that I really wasn't at fault (and none of the other 29 people on the rota had a problem), and that they had been very aggressive towards me, but I was shut down at every turn and told that they were going to speak to the leaders of the organisation to inform them of my incompetence and immaturity. 
Unfortunately the leaders of the organisation thought that I should just suck it up because this person was from a different culture and we should all just accept their "foibles". Needless to say I left soon after that (once I had fulfilled all my previously agreed responsibilities), and never went back. I heard the organisation folded about a year later - not surprised at all!