Elvis. When I was about 13 a friend's mom had an extra ticket and offered it to me... I turned it down. duh.
Heart. I had no idea the whole band was such a kickass LIVE act back in their radio hits days. Oops.
...and... I wish I had paid attention to more than just getting shitfaced when I DID attend Pink Floyd, Yes, ELP, and REO Speed Wagon concerts way back when. Kid hanging with the wrong crowd apparently.