I only played a GM once. Boris Kogan was his name, I think he was from Russia. My Uncle sat next to me. The setting was the local pub and there only about 10 of us playing Kogan. He beat all of us except for my Uncle. My Uncle was a heavy drinker and he and I both proceeded to get very drunk during the game. My Uncle played the Budapest Defense and got a draw in the end...
He used Fischer-style tactics on the GM, complaining about the lighting, and demanding more time to make his moves. I remember Kogan walking up to his board, and my Uncle--3 sheets to the wind--looked up at him and said, "What. It's my move?" Everyone burst into laughter, and then Kogan--with furrowed brow, looking down his nose, said, "It's ALWAYS your move!" .. and stepped over to the next board. Clearly, Kogan was *not* amused.
My Uncle could never win in tournament play because he took too long to make his moves. The clock--and his drinking habit--were the only things that prevented him from being a career chess player. He played in the US Open back in the 60s, and won 4 games at least. All of his losses were due to running out of time.