We gamed as a group and had a blast joking.
Are you sure it was Bitcoin and not Linden dollars or any other in-game token? Plenty of in-game economies existed back then.
In 2010 (I think), someone set up an L$ to BTC exchange inside Second Life.
You don't remember which game you were playing or the website you used to buy Bitcoin, but you are confident you remember the date. Explain this.