Costa and Thomas successfully fooling the cops, by way of hiding the entire party in the back, making them be quiet, and keeping them out of the house by citing law stuff they probably learned on television. And when they leave...
Costa: To the break of dawn, Y'all!
Thomas's acceptance of his party being awesome, despite all the shit he'll endure. He flips off the news cameras and then jumps off the roof of his house onto a bouncy house.
Despite the midget being an Ungrateful Bastard, him punching Costa in the nuts is pretty cathartic, especially since it's one of the only few punishments he gets throughout the film.
An earlier scene has Costa mocking Thomas to the camera while they're in the car. Thomas slams the breaks at a red light causing the camera to slam into Costa's head.
Watching the party descend from a simple gathering to an out-of-control mess and finally into a complete war-zone is awesome to behold. Particularly from the party-goers and police double-teaming T-Rick to the mad dash into the falling-apart house to grab the dog before everyone hightails it out of there.