Movies need parties to be cathartic or life-changing. Superbad treats getting to a crappy house party like an epic quest during which our protagonists confront each other with huge secrets they'd been hiding all year. House Party has that big house party. All of the characters in Can't Hardly Wait use the party as the perfect time to make public declarations of love or wild, out-of-character life decisions. The party in American Pie is the holy grail for our protagonists, all of whom have vowed to lose their virginity at that party, because the best part of having sex is thinking "Hey, my buddy is doing this too, cool."
"I hope Steve's having as much fun as I am. I bet he's smiling. What a cool guy."
But that's just movie law. Hollywood can't make a movie about a realistic party where a bunch of people laugh and drink until the police show up at midnight because the neighbors complained about the music, because no one would care about that movie. So instead they make Project X, a teen party movie where someone drives a Mercedes into a pool, someone brings a flamethrower, and the SWAT team is called.
In reality, the amount of fun you will have at a party is inversely proportional to the level of importance you put on that party.