I have this exact same problem with my partner. What kitana said is spot on. I disengage. I get the heck out of the situation. If I'm trapped in the car, I completely cease all conversation and just look out the window or read or something. I never try to help solve the situation because at that level of frustration you turn yourself into the target if you try to be helpful. I have to admit that it's gotten bad enough often enough that I'm on the verge of ending the relationship. The only thing that keeps me hanging on is that a few years ago he was laid off and during that period of unemployment, the stress evaporated and he was so happy and so pleasant. He smiled all the time. He was a pleasure to be around. At the end of this year he will meet the qualifications to go on my employer's health insurance. If he will accept doing that, he can retire. If he doesn't do it, I think I will leave him. I really can't take it anymore.
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
Starting squat: 45lbs. Heaviest squat: 180 x 2. Heaviest Deadlift: 230 x 2