I wish I could say I had a personal reference, but I have only ever seen him once, and he was anything but mad. He came to Dallas for the grand opening of the Nebraska Furniture Mart and held a public event and charitable auction at the retail location. I was astounded by how he managed to charm the crowd. He walked out on stage and stated that he wanted to sing the national anthem. As he approached his seat, he casually took the auctioneers cowboy hat and placed it on his head, which got a laugh. Once seated he produced a banjo from behind his seat and sang "The Eyes of Texas" (instead of the national anthem). He then turned the banjo over to the auctioneer, and the bidding began. As the high bid approached $19,000 with no takers remaining, the salesperson looked over his shoulder to Buffett in an attempt to continue the bidding war. Rather than pit himself against the audience, Warren just chuckled and said he would match it, but that the banjo should go to the lady in the audience. He then stood up, put the cowboy hat back on the auctioneer, waved and walked off stage. He was probably there for twenty minutes, and he owned the crowd.
As I watched him on stage, I recall thinking how none of this had come to him naturally. At fifteen, he struggled to fit in at school and read Carnegie's "" to learn how to interact gracefully with students. I think he has spent a lifetime learning how to work with people, and that even the events that likely make him mad are controlled.
My favorite example is his interaction with the founder of the Nebraska Furniture Mart, Mrs. Rose Blumkin (Mrs. B). When Buffett was making the acquisition he is said to have asked himself the following:
One question I always ask myself in appraising a business is how I would like, assuming I had ample capital and skilled personnel, to compete with it. I'd rather wrestle grizzlies than compete with Mrs. B and her progeny. They buy brilliantly; they operate at expense ratios competitors don't even dream about, and they then pass on to their customers much of the savings. It's the ideal business--one built upon exceptional value for the client that in turn translates into excellent economics for its owners. 
To put it lightly, Mrs. B was a formidable competitor. When Dillard's opened a location in Omaha they actually decided not to sell furniture because they didn't want to compete with her either.
After the acquisition, everything went smoothly for a while, but then the second generation, Mrs. B's children, assumed control of the business. Mrs. B complained to Buffett that they were not running the business as she intended. When he didn't respond, she moved across the street to open a competing business. Buffett's response? He went to visit Mrs. B and brought her two dozen pink roses and a five-pound box of chocolates. The two made amends, and Buffet bought her out a second time. (Note: I believe the second time he had her sign a non-compete.) When asked for her opinion of Warren Buffett only months before the second transaction, Mrs. B replied, "He's a real gentleman." 
Early in my career I sat in on a heated negotiation that was going in circles. Finally, one of the principals stood up, and in a very stern voice threatened to kill the transaction. He was very calm and controlled, and he got what he wanted. He told me later that controlled outbursts can be a tool if seldom used. My guess is that Buffett takes this to the extreme and that he prefers to substitute charm for anger whenever possible.
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