A website which allows people to share a credit card among many people (like 1000s). This way, you build up crazy points faster. They could have a giveaway each month to give the rewards to. Not only for credit cards, but for shopping rewards cards as well. Could be useful for kids/people without credit cards to shop online (as long as they pay up front) or for people who just hate being tracked. Certainly against every credit card company's policy but it would be cool to see how long someone could keep it going before they got shut down.
After re-reading that, sounds like the only people who would use this would be people who have no credit/bad credit and criminals... but just think of all the reward points...