One of my best friends sent me a link to the game and wanted me to play, at first I told him I'm not clicking one of his random ass links, but he finally got me to play. For the first bit I felt the game was rather stupid, but I played it with him anyway, and realized it's probably one of the best damn PC games ever.
September (or maybe August) 2010, my friend starting talking about this game. It sounded pretty awesome so I listened to him talk about it, one day he invited me over and we played it. I then went home and bought it myself.
Found about it long long time ago (I believe still in Alpha, not sure what was the version) through friends. I remember I bought it as it was cheap at the time (and they did mention that when the game was ready it would cost much more) but never really played it that much (I used to play a lot of FPS...) until like 6 months ago... Now its the only game i have played since then...
A friend of mine showed me it last year on my birthday. He downloaded the pirated version of single player just so I can see if I would like it or not. Few days later he bought me the full version of it.