On Friday I was walking around downtown Portland, looking for a place to buy a prepaid SIM card. Verizon had giant ads on various trains around town, and their's was the first shop that I spotted. I went inside and told the guy that instantly came to me what I was looking for. He asked me if I have a GSM phone. I reluctantly confirmed, not completely sure about my Nexus 4. He then went on about some gibberish about them not supporting GSM. Since my previous phone, the Nexus S, was bought in the US and I saw no reason why this shouldn't support whatever tech Verizon uses, I tried to argue a bit with him. Instead he put me on their waiting list, so that I could talk to someone else. My name appeared as "Jurn" on some monitor above the door, a little later along with "Chen" below (who I saw coming in as well). I killed some time with some silly iPad game, until noticing, maybe 20 minutes later, that my name had disappeared from the monitor. By now there was some other sales guy standing around, so I asked him about the waiting list. After some confusion about the lack of my name up there he just asked for I was looking for. Again, I said: "I'm looking for a prepaid SIM card". His brief reply: "We don't sell those."
Maybe the closest I ever got to yelling, cursing, or both, at sales people in public.