As a person with 40,000+ feedbacks and 17 years on eBay, relax as things will be just fine. If you deal on eBay, you are going to deal with "insufficiently_thoughtful_persons" and this guy, in my opinion was in the wrong and is just an impatient jerk whose life probably sucks as is taking it out on you. Ebay WILL NOT DO ANYTHING for you (this is a fact, don't bother trying), and them removing the negative feedback that you are able to leave for buyers was horrible and gave too much power to the buyer in more ways than one. All you are left is the ability to "Report The Buyer" and that report probably goes in the bin. But what are you going to do, not use eBay? I have been lucky to have less than nine negative feedbacks and about a dozen neutrals throughout my time on the site.
I had a guy in Georgia want to fight me because his item came three days late. I had another guy call me up because he wasn't able to understand the simplest of my descriptions (something a five year old can understand) and when I kept telling him that he doesn't understand, said that if I tell him this one more time, "he will break my jaw". I have more nightmare stories, but anyone that deals on eBay has a collection of them, I am sure. It could always be worse. It could have been a negative and simply reply to the feedback left and explain yourself, and next week I am sure the anger will dissipate. For the most part, 99.999% transactions go without an issue, but it's the small amount that do go array that seem to get us most upset. Good Luck.