My job here was to review certain reports that were going out to provider companies, ensuring there were no errors. However, we had to be sent these reports in order to review them, and as I was fast and good at my job, I would routinely be waiting around for hours for management to send me more reports. Management simply moved slowly, so even when I pestered them to send more, I would often have to sit around doing nothing.
One day, I decided I would take advantage of this downtime and do some freelance work while waiting for the reports to come in. One of the managers walked in and saw me on my laptop and told me to put it away, so I did so immediately and without question. When I came back from lunch, I was pulled into a meeting with the managers and was told I was being let go. Apparently, bringing your own laptop/tablet/etc/computer technology into the building is prohibited due to security reasons, and is cause for dismissal. This information was "in the employee handbook," a handbook which I didn't even know existed, and had never been provided.
So, to review, even though I had pestered my managers for work, had downtime, was one of the best employees on my team, had never had a negative run-in with management, and immediately acquiesced to the request to put the computer away, an un-promulgated rule violation led to me being fired on the spot.
The work was terrible and I was treated like a straight up monkey. Now I work in a field I love with clients and colleagues who respect me. Being fired from this job was one of the best things that ever happened to me.
There also happened to be two cocaine overdoses by employees on the premises while I was there (about a month).