What should i do if i'm, say, at a party and someone gives me a styrofoam cup?

I say you accept it, enjoy the drink. Not doing so would be rude. Just don't buy styrofoam, or when having your own party don't use it. Maybe they'll catch on....Besides, you're at a party lighten up....maybe they couldn't afford to serve in crystal..that styrofoam cup will not save the planet however, your being the one person who refused the styrofoam cup will totally alienate you