The main rule is this: If you are underage and drinking at a party, good deal. The point at which the rule applies is when you go to put pictures of that night on Facebook or any other social networking site. If you or anyone underage is holding a red cup, don't post it. Future employers and people's parents don't need photographic evidence. "Nobody believes it's just soda in your Solo cup."
Me: Damn John, yall got wasted last night.
John: I know man, put those pictures up on fb!
Me: Sorry bro, red cup rule. I don't need your mom bitching at me again.