I found a perfectly legal - and to me - ethical way to drop my employer right in it.
First, they didn't fire me, I quit. Second, I was hacked off with them because I'd been treated as a dogsbody, passed over for promotions, always got the smallest pay rise and eventually, after a long talk with another guy in the department, who told me - as I suspected - the big cheese of the entire site had it in for me, Idecided to go elsewhere. I landed a prime job with much better pay and prospects, and back to my preferred career as a CG artist. They wanted me to start ASAP but understood I had to give notice.
It was when I was drafting my notice that I remembered I'd not taken much of my leave; I'd recently divorced so I didn't want to spend time moping about on my own, so I had 16 days left. After a bit of checking and double checking, I confirmed I could use these days as part of my notice, so I'd only actually be working at my old place for 4 days.
The department head wasn't too pleased. "I don't think you can do this", he said. "I don't think you can stop me", I replied. He then scurried off for a talk with the HR bods, who confirmed I was in the right and they were up the proverbial creek without the legendary paddle. He then offered to buy back some of my leave entitlement, so I could at least get a new bod started on the right path. I told him there wasn't a truck big enough for the money I'd want in return. "Not very team spirited", was one of the things said to me about it. "Well, you buggers didn't do me any favours these past few years, so why should I do anything in return?"
Not saying the name of the firm, but they had a 3 letter name with an A at the start, an N at the end and an O in the middle.
Took a week of my leave enjoying the sunny weather with my new GF, then started at my new job and never regretted a moment.