I've always been one for etiquette, if there's a queue behind me I play 1 game and walk away. I remember though being utterly infuriated waiting to play a SS at a show, I walked up behind a girl who was playing single player but had put 4 games on the machine, I decided to wait behind her as you do.

She finally finished her 4th game (honestly she was pretty rubbish as most of her balls were lasting about 20 seconds, or coming back with the ball save) and she actually looked around, saw me standing there, and then put 4 more credits on and continued to play! Talk about ignorance of your surroundings. I gave up and played the game next to her until she finished. I didn't have the patience to say anything then but I would now.