The one that made me quit was when I was told I had to drive to the data centre and do a backup every day over the bank holiday weekend with no extra pay or time off. For no reason. And yes I know I'm an idiot for doing it but whatever.

The one that made me walk out, a month and a half later, was when I came in on Monday morning to discover that my boss had entirely rewritten the code I had spent literal months on in one weekend. Naturally he'd broken it and said it was an improvement.