I would call him back. Let him have his say. Then simply say, "Thank you. I appreciate your apology. Is there anything else I can do for you today?" In other words, stay professional. Remember this is a business. This crap happens all the time. The cream always rises to the top and your bosses will have a new found respect for you if you accept his apology and move on. This attitude shows a lot of strength and character. I'm sure you are not the only person he has ever treated this way. You don't have to be his buddy. But represent your company with class and dignity no matter what.
