Simply stated boundaries help. First you have to get them clear in your own mind. If your boundary happens to be "I will not argue with you when you have been drinking," then you don't consider the boundary crossed simply because the person is drinking. When the argument (or attempt to provoke one) starts, you simply say, "I will discuss that with you when you haven't been drinking," and walk away.
That's detachment--it is refusing to engage the drinking behavior.