I had a moment like this once. I was having a good day, didn't face a block up until then. It was just two more guys with me and we were talking about some random shit. And then suddenly boom.... I get stuck on one word and prolong it uncomfortably. Both of them chuckled but then I moved the conversation. I didn't show it but the embarassment killed me for a few days. It's weird how a situation as trivial as that still comes back to me when I'm upset.