That seriously sucks. I was in a similar situation, only it was with a friend of 20 years and we were able to talk through the issue and now we're closer than before. Maybe if you let cooler heads prevail for a few days and tell him/her that you want to talk about it, they may be receptive to it and you'll make it to 11. If not, I wouldn't call them much of a friend, TBH. I mean, if you've known someone for that long and you can't work out a difference to keep being friends with them, what kind of friend are you really?