This is from the inside of a book, Aragones 3D, but legendary Mad Magazine cartoonist Sergio Aragones. It was the mid-1990s, and Roy Trubshaw and I were at Gen Con in Milwaukee. We were walking back from somewhere together and saw an unmanned stand set up for Sergio Aragones. We both knew his work, and couldn't believe our luck when he suddenly materialised and sat down just as we got there. We gushed how much we liked his work and each bought a copy of the book he was selling. He asked if we'd like it autographed, which we hadn't really thought of because we actually wanted the book, not the autograph. We said yes, anyway, so he autographed it then added a cartoon of himself drawing it. As it was a 3D book (with red/blue glasses), he signed it holding two pencils in his hand at the same time. He did a copy each for Roy and I, which took him a little time despite the fact that he's often referred to as the world's fastest cartoonist. We thanked him and moved on. I don't think anyone had formed a queue after us, we left him sitting alone.
Nowadays, people would be asking for a selfie with him. They perhaps wouldn't get the 3D signature, though.