I've had some experience trying to be careful talking to someone with a short fuse. Here's what I learned: Don't bother being ultra careful. They're going to blow up sooner or later anyway. You will never succeed in treading likely enough on those eggshells. The kid gloves you wear when handling this person will never be soft enough. You just condition the person to expect you to tie yourself in knots trying to avoid setting them off.

Maybe it's time to throw a fit yourself. Raise your voice and say, "I'm sick of you being mad all the time. Now I'm mad. How do you frigging like it?"