The success of Cards Against Humanity is evidence of massive demand, and yet all they have protecting them is their brand—unlike, say, craigslist, whose unwillingness to innovate is legendary but whose business benefits from massive network effects. As a result, the (apparent) apathy of the Cards Against Humanity founders offers an opportunity: copy their basic idea, for which they have no protection, and structure your new venture as a real business with full-time efforts devoted to growing sales. You could even one-up them by dropping the non-commercial clause in the Creative Commons license, allowing potential partners to profit and thereby grow your brand further.

The Cards Against Humanity guys are leaving money on the table. Who's going to pick it up?