I must warn you: It's not easy! A whole lot of time you will end up frustrated with your attempt, and other time, you wish this person would just go away! You'll feel the defeat, but if you are persistent and strategic, you will eventually get through. Some tips:
1. Keep a positive mind and thoughts - if your mind is already clouded with the idea that you can't communicate to this person, big chance you won't be able to do so!
2. Listen; don't just hear what they say :) and remain open to chances where this person softens up
3. Stay calm; control your voice, breathing, and posture to a less defending/offending way, and bring about a wave of openness - if they yell, don't yell back
I'm very sure there are other tips. These are the three that are deeply embedded. When nothing else works, I just bless the person silently and move away. Try again another day...