Mine was 2 parts at the same job:
1) Got to work at 6am to work on a project that had all kinds of issues due to the onboarding team, the client, and our GM. Worked all day with a counterpart 1,500 miles away until 10pm missing the college championship football game, then spoke with this person all the way home until 11pm to prep for the next day. Worked 7am to 8pm with him again and got things sorted to fix all the mistakes everyone else had made. The nest week I put in my vacation time for 5 months later that I had discussed with my boss 2 months prior to be told "well, you had better get this account fixed or I am going to deny your vacation time." This being after we just put a $2,000 non refundable deposit on air, hotels, villa, and transportation. I still went but caught shit the account wasn't being handled done right, but nobody else had any ideas to improve what we created including the GM and OPs Manager that set up the disaster.
2) I had been busting my ass for 70+ hours a week working with a team of temps trying to fix things so many people higher than me had set up broken. GM's, sales team, etc just lied to get the contract and then dropped the trash on warehouses and myself. After a year of this they decided to grow the team 25%, instead of temps have all college degreed professionals, and move the whole operation 1,200 miles away. They then had the nerve to ask me out of "professional courtesy" to stay on and not leave so we could train my replacement, his assistant manager (I did not have this position on my team), and have my team train their whole new team. They offered me a decent severance package but not my team, so in a private meeting I let my team know I would be seeking employment elsewhere and would gladly be a reference for them if they wanted me to. To this day (8 years later) I still wonder if I should send a glitter bomb or box of wild animal scat because of pure hatred.