just assume that every time you pug you will be playing with utter idiots, that way you will be happily surprised when they do better and less mad when they conform to your expectation.
I hate when I am cloaked and some one decides they should stand right by me while I cap, drawing the mobs to me. Even worse when they got bad aim and they kill me, even worse when said player makes me use a gel when he runs off after that...