Mine was Gary Wright (you know, "Dreamweaver"). I had no clue who he was, but I wanted to go to a rock concert. I was maybe twelve or thirteen, and I had fun.
The next was a little more memorable: Aerosmith, and an opening act nobody had heard of at the time. The lead singer split his pants partway through and had to leave the stage; the guitarist, some guy in a cap and shorts, covered with a long solo. The singer came back out with the split held together by a prominent figleaf of gaffer tape.
A few months later, when the band's next album came out, we all thought, "Oh, THAT'S who they are". The album was Highway to Hell.