What the hell is a party foul?
Like any foul (as in those in sports not as in birds), this is an action that goes against the generally accepted rules of a party. These may be punishable by the group you are in.

Okay. Examples?
If you see a party foul, yell "party foul" and bring attention to who did what.
Spilling a soft drink, beer, etc
First, the spill must be cleaned up to the host's satisfaction. After the spill is no more, everyone who was in the room gets to punch you in the arm.
Tripping over the keg
You'll first get laughed at, and then be told to sit down for ten (10) minutes. You will most likely be put somewhere away from the main party and the opposite sex. Depending on how drunk you are, you may be asked to sober up for awhile.
Spilling the bong
First, clean the mess (make sure to get any weed product off the floor). Second, use carpet freshener to mask or remove the smell.You gotta drink the rest of the bong water. If there is no more bong water, you get two (2) hits from every partier in the room. So if you spill it, you'd better get it all.
Hitting on someone else's girlfriend
Ouch. You'll first be embarased, and then depending on the severity of the foul, you will be punished by the boyfriend. (Just don't start a fight or make an enemy)
Being loud or yelling "cops"/"police"
The host gets to give you one (1) punch to the stomach. You may be asked to stop drinking or leave.
Puking/throwing up
Stop drinking. Clean it up if needed. Sober up. Get a ride home. Make sure not to puke in the car.
Trash talking/Fighting
Offensive party is sent home and often banned from the host's house and parties. The defensive party is given a punch by the host anywhere but the face. The defensive party may be asked to leave in some cases.
Stealing from the house, the tap, anyone else
You'll get searched for stolen goods. Stripped naked (or to your underwear). Kicked out and banned from the host's house and often other people's too. This may result in a fight, but it is not encouraged.
Calling the cops out of spite
It's one thing if something bad really goes down, but calling the cops out of spite is just not cool. You'll most likely not go to a party in your area again. You will also most likely be beat severly about the head and face region.
Drinking and driving
You risk getting a DUI/DWI charge, losing respect of your peers, and even your life. Just don't do it.
Ouch! That's no good
Yeah, don't be an ass/idiot/prick/loser and you'll be fine. I mean we've all most likely commited a foul or two (2) in our life, just don't do any of the major ones or commit too many of the minor ones.
Have any other rules or punishments? I'd like to get a /msg if you know of any. Don't have any? /msg me anyway!