For me, it was Jethro Tull in Louisville Gardens, late 70s. They played their sets and went offstage without playing Locomotive Breath. No one moved and they returned for an encore. But it as “Living in the Past”. Went offstage again. This time the lights came up and the roadies began disassembling the equipment. Everyone was both pleased and bummed. The concert was fantastic but we hadn’t heard one of their best and most popular songs. About the time people stood and just started to make their way towards the doors, the keyboard player walked onstage. He walked right to the edge of the stage wearing a tux coat and a huge grin. He raised his arms and the sleeves fell back. In this pose, he walked over to the piano, sat down, and began playing the solo intro to Locomotive Breath. All the while he was playing, the roadies were feverishly reassembling the audio gear and returning the instruments. Just as he finished the lead in, the rest of the band returned and they played to stone silent audience in a fully lit concert hall. When they finished, the place went nuts.