It doesn't really matter. If you know about a party, you're as good as invited, unless you've been explicitly told otherwise. People who aren't wanted are kept ignorant.
If you're throwing the party, go ahead and invite them. Depending on where you live, you can probably predict whether they will show, but overwhelmingly they won't. However, by warning them, giving them your phone number, and interacting with them while you're sober or only slightly stoned, you've already given yourself a lot of rope. Any decent person will call you before they call the cops. And if they do actually come to the party, they should absolutely feel welcome.
Obviously, wear whatever you want. But if there's a theme, costume, or other particular request, abide by it. Smart party-throwers will be vocal about the fact that people not in costume won't make it through the door. Sounds harsh, but people need to show more respect for ritual.
If you have any money on you, cough it up. Even coins are appreciated; it's a symbolic gesture of solidarity, and builds community. If there's naught but a breeze blowing through your pocket, don't stress. Simply assess the situation: are there fine women walking around with trays of martinis and cigarettes? Or is it a dim basement with a keg shoved in the corner? The amount of effort shown on their end can dictate the amount given on yours.
Do not say you are having a party and then not provide at least one keg or some equivalent. B.Y.O.B. parties are okay, but need to be aggressively advertised as such.
It is strongly recommended that you employ a "keg master." It's nice to have someone who looks physically intimidating, but it's essential they are entirely non-combative. Simply having someone there to monitor and assist pumping and pouring will help keep everyone in line. If you can't find a keg master, the space around the keg is a lawless place. Be alert, assertive, and defensive.
If there's someone playing DJ, leave them alone and let them play whatever they want, unless they ask for your consultation or requests. If there's just music playing, the general rule is not to take it upon yourself to change it, unless it's your party or you have permission. The exception is that if you have majority support within the room for what you're changing it to, it's cool.
Live music drastically increases the chances of legal involvement (see below). If you choose to have live bands, make sure that they know they are entirely responsible for their own equipment. As a partygoer, you aren't obligated to watch the bands, so it's better to leave than to boo.
Once the cops show up, it's time to organize. The party throwers need to decide if they think telling people to go inside will work--it usually doesn't. Don't even try it if there isn't someplace inside where people can smoke. Another option is to kick everyone out. In that case, everyone should obey. The bottom line is that fines and other legal hassles are a bitch, especially nowadays.
If you don't want to share your pot, don't bring it or bust it out at a party. This is another community/ritual issue. Smoking pot in front of people and not offering it is aberrant behavior, and rude. However, feel free to get high in your car, in a sanctioned bedroom of the house, or a secluded corner of the yard, with however many particular people you want.
A sticky one, because it makes everyone more of an asshole. One common error is doing coke in the bathroom. The only right way to do this is either alone or in pairs. If you're alone, don't dawdle, which is easy because there's nobody to hear your brilliant effusions. In pairs, one pees while one snorts. It shouldn't take any longer than if you were just two people taking pees. Unlike weed, you totally do not have to share your coke with anyone, and it's universally accepted to pick and choose coke partners, then take them to a "VIP" or "coke" room. Just be absolutely sure that all residents of this room want it to be the coke room.
The bad thing about good parties is the bathroom line. Men should piss in the yard. Unless it's raining/hailing/snowing, then they can come inside if they want. But they should piss in the bathtub, sink, or shower while a girl is pissing on the toilet. If you think that's gross or inappropriate, grow up. It's the most efficient use of time and plumbing and won't do anything Bon Ami can't fix.
If you have to poop at a party, don't try to "hold it." Just poop. Specifically in the toilet (for everyone, regardless of gender).
Pick It Up: By all means, dilute yourself with alcohol and hit on people you're intimidated by. If they're interested, they will usually make it easy for you once you've signaled the attempt. If by the fifth attempt, you're still doing all the work, stop. No, really. Stop.
Making Out: Making out at parties is totally fine. Some people like to act grossed out, but that's their hang-up.
Home Base: Actually having sex at a party is more difficult, and it's not recommended that you do this with a person you've never slept with before, especially if they're drunk. Again, legal issues suck. But if you've "known them" for a while, you can. As long as it's not in someone else's bed, and you don't honestly care if someone barges in on you.
Obviously there's nothing you can really do in the immediate sense if you're passed out. If you're with someone who passed out, just make sure they don't get raped or ripped off. Beyond that, just let them sleep. Plus, if you're bored, and you think they might not kill you, draw a mustache on their face.
Unfortunately, alcohol sometimes causes hissy fits. People burst into tears, wailing about what is invariably some kind of romantic issue. Parties are for a good time. These people need to be removed.
BARFING & BARFERS
GodÉ If you have to barf, do not head towards a toilet. It's the rudest thing to take up residence with your cheek on the toilet so nobody else can use it. And once you've assumed that position it can be hard to leave. The best-case scenario is that somebody will schlump you over towards the bathtub, where you will spit onto your shirt and pretend to sleep while peeing people parade past. Do not be this wretched fixture of the can.
If you're with someone who's puking, you get to play nurse. That is what friendship is for.
Sometimes people do crazy things when they're drunk, and that's funny! If you wake up and find that you've stolen someone's stuff, give it back while making self-deprecating jokes about how wasted you get.
The main thing to remember is not to jostle other people. So, like shoving isn't good unless you have a great deal of space around you. Try keeping it to sharp jabs at the heads and torsos.
A tip for the party thrower, especially if you notice tension in the atmosphere, is to announce that it's time for the bare-knuckle boxing tournament in the backyard. Either plan on it or pretend like it was planned. Everyone wins.
It totally depends on how they die. However, if it's your house, you gotta deal, unless you're the one who killed them. That's what sucks about hosting, and why everyone should throw down respect for the host.
If you're a guest, you should probably leave, unless you're with the corpse.