My first vivid, indelible gaming memory came a few years after I'd actually started gaming. Everything before then is "there was an NES/an arcade cabinet and I played it", but nothing I could tell a story about.
Anyway, cut to the summer of 1989. As anyone who's ever been to Boston in the summer knows, you can set your watch by the afternoon thunderstorms. My brother and I had prepared for just such a moment and said "when it starts raining let's all go to our house, we're gonna show you something cool."
As expected, it started raining right around five, and the whole neighborhood (about a dozen boys aged 8 to 12) assembled in my mom's basement where the NES was set up. A few blows on the cartridge and Contra was ready to go. My friend Jared made the first key observation:
"Don't you know about up up down down left right left right B A select start?"
Said my brother: "You don't need it if you're good. Just watch." (this would become a catch phrase among our friends for a couple of years afterwards when we played sports against other neighborhoods)
My brother and I then proceeded to beat Contra in front of all of our friends from the neighborhood without dying once. Said Jared: "How did you do that?" Said my brother: "We're the Doucette brothers. We're just awesome." Coolest thing a ten-year-old kid has ever said as far as I'm concerned.