This is one of those expressions that can completly catch people off guard. It stands for "for the win" and nobody that has ever had sex (no, that steamy chat conversation you had with that sexy girl that was really a hairy old man doesn't count) would get what the fun of over using that expression would be.
FTW is incidentally a biker expression for [Hi Angie] The World and with a little hope they will take this theft seriously and take their anger out on the internet geek community.