Ok, I'm not going to make this very long because I think the specific details of my game may get boring and I think the general idea is more interesting. Also, you may all have input because this is a common issue that can be related to for those in college.

I think a really interesting Social Impact Game would be one that addresses drug and alcohol use. No one really knows how much one night of drinking or taking one pill of Ecstasy can really affect them, so wouldn't it be educational and beneficial for people to have that information in a game? Yes, I agree that people can learn it by reading books and asking doctors, but there is definitely a majority of people who retain information more efficiently when they are actively learning and interacting with the material.
What if you were a character in a game, and instead of "Fatworld" where you see how food affects you, you would navigate through your virtual life by accepting or rejecting events and substances, like marijuana or a night at the club with X amount of drinks. Maybe you would have a split screen that shows your brain on one side, and their your navigation screen on the other. As you drink more alcohol or take more drugs, your brain will be highlighted in the places that are being affected and hurt.
The reason I got this idea is because I was thinking about an MTV "True Life" episode on binge drinkers. The people were shown the brain of an average 18-21 year old, and then shown theirs. It was startling to see how big of a difference there was...