Since I just went through being fired and looking at unemployment, I think I have something to offer here. If you quit, you will have a hard time getting unemployment. You need to prove that it was a hostile work environment. Keep notes, quotes, and all written things. Write down and copy whatever communications you have, try not to have oral conversations. A hostile work environment is grounds for a lawsuit, but know you'll probably lose your job in the process. I'd try to shine the guy on as long as possible to find out exactly what his issue is. If he is your boss, even those higher up will maybe take his side. If you are downsized, you can get unemployment no problem.
The issue my employer now has is that they fired the disabled. It's a big no no. They also put down my doctor's appts as reasons for termination, although I have plenty of emails, cards, etc. to back up all the thanks I got for my job. No warnings were ever given. They were aware of my condition. I've spoken to a lawyer who says I will win a lawsuit, and believe me, I AM filing one. I wish you luck in this stressful time.
Jag