Cards Against Humanity

The "party game for horrible people" has sold over 30 million copies despite (or because of) being deliberately offensive. One player reads a black prompt card; everyone else plays their funniest white response card. There's no strategy, no skill, and no way to play it sober at a family reunion. The company has spent Black Friday money digging a hole in the ground, bought an island, and paid for the entire town of South Padre Island. As a game, it's barely one. As a social lubricant and conversation starter, it's unmatched. Available as a free download (Creative Commons).