This is going to be super-biased, the reason being, I have only played 3 games at a conventions: Doomtown CCG, some LARP, and Blue Planet.
Since this is all about RPGs, that leaves the post to Blue Planet by default.
Up until that time I had been to Archon many times, and stayed out of the game room as a participant. I had only been in there to browse, playing most of the games in the hospitality or open gaming areas with people I already knew.
I had always looked over the game sheets, due to arrival time at the convention everything that I wanted to play had already been filled.
At this particular con a few of us decided to get into a game together, and lo and behold, BLUE PLANET! One of my friends had the book and we had played it once or twice, he wanted to see how other people ran it.
So we signed up.
And were greeted at the table by one of the writers.
A quick perusal of the rules and character sheets and we were ready to go. Outlaws caught in media res stealing something from a transport. Wild West style on a water planet.
More fun than a barrel of monkeys, and ending with two of us in a standoff against the GEO, the police.
Standing inside the door to our transport, light flooding the compartment from the spotlight focused on our door, all it took was a look, no words spoken.
I went for the spolight, he went for the ground troops, and both of us went out in a blaze of glory!
The GM, Jeffrey Barber, just looked at us. "I have run this adventure many times, nobody, NOBODY stood up to the GEO!"
Good times had by all. Yes, it was a TPK-1 day, but it was a lot of fun.