I've only ever had one job that I really hated, but fuck was it a horrible experience. To think I turned down a pretty good offer from someone else to take it...
I was the 9th person to leave in the first 4 months, and despite leaving with practically nothing in my bank account, it was the happiest day of the year for me. Before that, I could feel myself slipping into survival mode - just switching off emotionally, not wanting anything to do with anyone. I was working 6 days a week and every Sunday was poison because I knew it'd start again when i woke up.
Actually, come to think of it, it's probably about 9 years ago this week that I walked out of the place. Needless to say, life has been much happier since then.