Soo, I have heard that alot of people has been very rude and offensive in pugs, and we certainly don't like that.
But I have the solution for you, you can find everything about how to behave in a random in this little guide.
1, Rolling on gear for another spec; since it's the start of Cataclysm, the dungeons and heroic dungeons are way harder than they've been for over one and a half year which makes it harder to get the gear you need. Many people are farming for gear these days and they get very upset when they've been farming a dungeon or heroic dungeon for a long time and a person needs on the gear they need and wins it. What am I trying to tell you, you say? Well, I'm trying to tell you that when you or another person needs on an item for a different spec and wins it over a person who needs it for his main spec, he will probably be mad. If this happens to you or someone else, try to write happy stuff to avoid problems, or ask gently for the person to give the item to the one who needs it for his main spec so you can get more justice points and buy some gear.
2, Wiping; if your group wipes and starts blaming you, just say that you're sorry or try to explain them gently what happened and how the whole group can do better next time. If someone starts to get mad and you can see that you can't avoid him going on a rampage, try vote kicking him for offensive behaviour or just leave the group right away to avoid problems. If the person who made your group wipe starts yelling and blaming everybody else, try to tell the tacts again, if he gets even madder, do as I mentioned above.
3, Ninja pulling; if you or someone in your group accidentally ninja pulls and the group dies, try to spread happy thoughts and say that it's ok and that it probably won't happen again and you're gonna down it the next time, people usually don't get mad over this.
4, Someone forgot to do a buff; just ask gently if he would please buff the group, if he does not respond he might not have seen the chat log so you don't have to get mad over this. Instead try to stand still and possibly make the rest of the group do so too, if he writes something in the chat, you can again gently ask him if he could please buff the group, if the person gets mad, just leave him alone.
5, People fighting; people usually get mad if you try to get involved in a fight, so just leave them alone and let them sort it out themselves, but of course, if someone crosses the line you can kick him for offensive behaviour.
Note: if someone gets mad or goes on some sort of unstoppable rampage, you can also start typing smilies since stuff like "UMADBRO?" can enrage them, causing them to do stuff like this, and remember that their mom is not always home to interrupt a third world war, you can also ignore them since they'll forget what happened pretty fast.
I hope you learned something from reading this (or if you're a very calm person, I hope you agree with this) and I hope you're gonna get some happy pugs.
Oh, and may your rolls be high and your loots be phat.