If you raid a lot, you get used to certain things. People are expected to be familiar with their class, their role, and the talents used to accomplish said role. You keep your gear for your main role current and also it's a good idea to keep your offspec gear current as well (you never know when you'll be switching). You know the fights as best you can. These are almost hardwired assumptions that build up into dogma over time.
They have no place in the five man random PuG.
I am not arguing that you shouldn't do your best if you're running a pick up group. I'm arguing that you have no reason to hold the other four people to a standard of play they haven't signed up for or agreed to. Clicking a role in the random window is not the same thing as filling out a guild application. A lot of these players are learning the game by playing it: it's not fair to assume they're reading theorycrafting sites and working their gear always with an eye towards maximum performance. The prot warrior in the run I just mentioned? He was a decent guy, picked up WoW last year, plays it when he's got time. He heard that Prot was OP for PvP so he went Prot, doesn't know the talents very well (he played some in BC but then they changed everything on him) and was very excited when I mentioned various sites he could go to for better information on spec and gear.
Not every 'bad' player is really a bad player. Some are just players. (Some of course are very very bad. Then again, there are very very bad players in raid guilds progressing through content. It happens.) These people didn't make any kind of commitment the way raiders are expected to just because they signed up to a random with you. Would it be nice if they knew not to stand in poison clouds or to know which attack they should be using in their rotation? Yes, it would. But going crazy and posting meters and ranting accomplishes nothing.
Also, to be honest, sometimes it's the 'elite raiders' that hold heroics back. Take, for instance, the DPS who brags about putting out 7k DPS in Halls of Lightning. First off, the mobs in HoL die so fast that the only way you're putting out 7k DPS is by attacking before the tank has even sneezed at them, which means the tank (often me) hates you with the fire and intensity of a thousand suns. Yes, I managed to pick them up with Challenging Shout and spammed every threat move I could even think of while desperately trying to generate enough rage to keep it up, thanks for the carpal tunnel syndrome. We don't need 7k DPS from one player to get through HoL. Secondly, that 7k DPS was only achieved because things died before other DPS could hit them, because again, you're attacking before the tank. You're not a good player because you put out more DPS than everyone else when you do it in this manner.
5k DPS and remembering where MD or Tricks are, using utility abilities, and waiting for the tank to pull is vastly preferred to going hog freaking wild, popping all your cooldowns as soon as they're up and otherwise being a jerk, much less then posting your hyperinflated DPS meter and waving it in the faces of the DPS you consider sub-par. This goes for tanks, too. I've been the tank putting out more DPS than the undergeared DPS in the run I'm on. You know what? Nobody cares. You're highly geared, that dude's using the quest axe from Zul'Drak. Cut him some slack, and in so doing, cut yourself some slack.
You are not there to police everyone else's gear, spec and playstyle. You are not there to have to micromanage every aspect of the game. You are there for emblems, maybe some gear, and frankly it's too much time and work to expect everyone you PuG with to play the way you do. You'll be happier if you just play, ditch when you just can't take it anymore (people would much rather wait for a replacement than listen to a tirade about how awesome you are) and wait out the time until your next. Or go do something else. People who sign up to a random didn't sign up for boot camp in your private How to WoW seminar. If you can't be helpful, at least be polite. Getting worked up over a random PuG just ends up with you worked up. You'll probably never see those people again. If you end up with a hunter who tells you he doesn't have MD because he hasn't been to a trainer since level 60, it's really not going to magically fix things to scream at him over it. If he'll listen to you and you can explain what he can do to improve, great. If not, let it go.
This is a lesson I struggle with: let it go. Your expectations of other players who you do not know, have never played with, and may never see again simply cannot be as high as when you work progression raid content or blood will squirt out of your ears and nose. It's messy. There's nothing wrong with trying to be helpful: if you see a player making a mistake you might have made yourself once upon a time you can certainly try and politely suggest ways they can improve, if they want to. But don't expect them to do so simply because you say so, and don't get invested in it: they don't know you either. They don't owe you any more than you owe them, their best effort to clear the run smoothly.
Trust me -- in the long run, your blood pressure will thank you.