Disabling music ruins the mood. Visitors dance and speak to music. It ends the party. One forum member worked at a bowling alley and turned the music off after cosmic bowling to get people to leave.
Everyone has seen a drunk person argue with anyone who will listen at a party. Aggressive guests are unwelcome, thus the celebration frequently ends when someone goes too far.
When the liquor runs out, it's time to call it a night (or get ready for the next get-together). It's a universal sign that the night is over but that everyone had a nice time.
This atmosphere-killer goes hand in hand with rude partygoers, but if someone over the line and a fight breaks out, other revelers will want to leave the area as soon as possible.
Fights, whether they are physical or just yelling bouts, will ruin the atmosphere of a party. In the event that said guests are not asked to leave, the other attendees will most likely leave on their own accord.
The presence of law enforcement at any party, legal or otherwise, can dampen the mood. Your party could have to stop earlier than you had hoped if neighbors file a noise complaint.
Cell phones are fantastic because they let us stay in touch and access the internet. This isn't always good. A party is over when someone pulls out their phone and starts showing humorous videos or casting them to the TV.
Since they have nothing to lose, uninvited guests frequently act impulsively. They might go crazy since they're alone. They also convince the invitee's friends and acquaintances to leave early.