A party where the beverages, usually beer from a keg, are served in red plastic cups. see kegger

Those porno videos like "College Fuck Fest" or anything like that when two people are having sex in front of a group of people at a party and they are all holding red cups.

a typical party where everything that is being drank is poured into red, plastic cups. this is a stereotype, not a fact, but it is still very common amongst college and high school students.

a party where alcohol is served (often from a keg) in red plastic cups, usually attended by college students

Similar to 'Thats what she said' but more sophisticated grown up, party slang. Used especially when alcoholic beverages are involved and they are disguised in red party cups.