AKA Smoking Etiquette, Weed Smokers' Etiquette, Pot Smokers' Etiquette, Marijuana Etiquette, etc etc. Compiled and edited from the various incarnations of this document floating around the Web.
1. The person who rolls the joint, no matter whose weed it is, gets to spark up the joint and get first hits.
2. If someone rolls a nice joint, it's good to give the person a complement on his rolling skills.
3. Never bogart. (What does "bogart" mean? Well, if you've ever seen Humphrey Bogart in a movie, he always has a cig going, but he hardly ever takes a hit. To "bogart" a joint, then, is to waste it by holding it while talking or whatever, and letting it burn to no one's benefit.)
4. Never put the whole roach in your mouth and get it all sopping wet ("duck arse" it in British parlance). That's disgusting and it messes up the joint. Likewise, don't put the whole mouthpiece of a bong in your mouth and slobber all over it.
5. If someone starts bogarting the bowl and starts using the excuse that it's okay for him to bogart it since it's his weed, this is definitely not cool. The punishment depends on the quality of the weed and how much he put in - if it was real crappy and he was real cheap with it, then you bug on the person and rag on him. :-)
6. If someone is too palsy to light the bowl, due to being too stoned or just being a retard :-) then they must relinquish control of the lighter to someone more able to get it lit. Note: this does not mean the person who lights gets free hits; this privilege tends to get abused ("Hey, lemme light it for you...").
7. Never ask for a joint or call two's - wait until the joint is passed to you. However, this rule may be broken if someone is obviously abusing the trust placed in them by the other smokers.
8. If someone is so much of a palsy that they blow into the bowl and fire the contents all over the floor, this person must be ragged on and the person can't smoke on the next round (unless it was his stuff).
9. Never make fun of how big a hit someone takes. Each person has their own lung capacity and knows how much they can take. It's their fault they didn't take a big hit. All the more for you! (Then again, if you're all veteran smokers, you may have an excuse to poke fun if someone is smoking like a wuss :-)
10. If you smoke with someone in your house, you should let them eat some munchy food that you may have lying around. Don't be cheap with your food if you have food.
11. If someone who's smoked asks for a sip of your soda, you must give him some. Drymouth is not fun.
12. Converse of the above: if you ask for a sip, don't be rude and take a large gulp.
13. If you're smoking from a bong and there's not enough in the bowl for a whole further hit, finish it off, but then refill the bowl. Note also that it's very impolite to hand someone an empty bowl without telling them about it. A proper warning would be along the lines of "Here you go... I think it might be cashed."
14. Never bitch about someone else's weed being no good. If you don't like it, don't smoke it, my friend.
15. Don't ever push someone to smoke weed. It's their choice.
16. If a friend gets you high, then sometime in the future you need to get that friend high. C'mon, that oughtta be obvious.
17. Share the wealth to the needy. Remember that time you had lots of weed, but now you don't? Well, if you shared your last stash with friends, they'll be sure to get you high this time around.
18. The Cardinal Rule: Thou shalt not turn down a smoke.
19. Always offer to match someone if they offer to smoke you up. Even if you only have shake left, offer to throw it in... it makes those who buy weed a lot feel a little better.
20. Phrased in the form of a narrative:
OK. My buddy and I are sitting around smoking the weed that I just scored. After flaming-up, and taking a few moderate puffs, I pass it on. The sounds that follow can only be described as vacuum-like. After an a couple of huge, lung-busting tokes, the guy passes back the remnants of something that could have, at some point, been a joint. If it's not completely "canoed", then it's absolutely soaked. I not-so-subtly drop that old Cheech & Chong line "Hey man, can I wring it out for you?" He just looks at me.
21. After smoking-up, the odd "crass-monkey" will actually eat the stained, disgusting roach. This must be because they want that "extra bit" of oil, resin, or whatever's left on the paper. This situation can be compared to the patron of a good restaurant picking up his "as good as empty" plate and licking off the remaining morsels of food. Sure he got that little pool of gravy, but was it really worth it?
22. You get a shotgun, you give a shotgun.
23. If you buy weed from a friend or a friend of a friend, it is polite to roll a joint - a small one, if you wish - and smoke with the person who sells you the stuff.
24. The person who fills the bowl is given the opportunity to take the first hit. It doesn't matter whose bowl it is.
25. If you're going pack a bowl, pack it fat. Tiny's no good to anyone.
26. Always remember to thank a person who has gotten you high. If people never say thanks it gets a little annoying.
27. The person who brought the bud picks the music.
28. When smoking in a car, the driver gets to choose whether or not you bake it out. Hey, if you don't like it, get your own car.
29. Again, when using a bong, don't blow out the ashes, unless that's what the "homeowner" does.
30. Never go to someone's house expecting them to catch you a buzz. (Of course, there are exceptions to this rule...)
31. If you spill the bong, clean it up - and don't forget to put water back in it!
32. If the bong is plugged, always clean it out before passing it on.
33. Always clean up after yourself, especially if you're in a place you can get caught (your dorm, house, car...).
34. You should obviously try not to knock the cherry out of the joint (and you wondered why a big joint is often known as a "bomber"?) and drop it somewhere that it'll burn a hole in something, but if the unthinkable happens, you should always own up to it. It could be the source of great embarassment for your friend if their folks find it without them having a prior excuse.
35. When the roach gets too small, if someone has a problem with it, it's common courtesy to put the roach in a bowl and finish it like that, as that way the people who don't mind burning their fingers don't get it all.