Easy, for me it was PONG, and no im not trolling anyone here, when i was about 5 years old my father brought home a shiny new PONG console, (i think it was called familivision) and it had 2 player vs mode, my and my brother played for hours this was in the mid 70s, the console was so rudimentary that the "controlers" where atached to it, it run on batteries and the sounds (bip and bup there was TWO of them) came from a little speaker inside it, great times, years after that came mariokart on the snes (countless hours) and then the absolute kings of my childhood Mariokart64 and Goldeneye (countless broken controllers), my first online multiplayer was starcraft.