"Dude, that's like the fourth Blinkstrike I've gotten this week. You want it for your rogue? 'Cause otherwise I'm just vendoring it."
Everybody knows someone to whom the game's random number generator is stupidly generous. I've known people who have nabbed practically all of the rare dropped recipes and noncombat pets without even being aware that these things usually require effort. Others can't swing a dead cat without looting a world drop. I'm not one of these people, but it sure pays to know someone who is, because these people practically never fail to cause rare mounts, pets, and drops to rain from the skies wherever they go. If you can't get groups with them, try to be a person who springs to mind when the 1,458th Design: Solid Star of Elune drops for them.
Not a valid statistical assertion? I care not. There are some people out there whose ingame luck absolutely beggars explanation or belief. I don't question it, I just try to be a boxcar on the gravy train.
5. The Cynical Raid Leader
"Look, the reason you keep dying "randomly" is you're not facing the same direction your healer is. You're going to keep getting Air Burst out of her range, and you're going to keep dying to curses or Doomfire as a result. It is not her responsibility to run all over the place trying to find you; it's your responsibility to stay in range. Cut the crap or I'm going to have to bench you."
Raid-leading, particularly on progression content, can be a pretty ugly job. You have to do whatever job you already do in raids to the best of your ability while keeping an eye on what everyone else is doing, to the point where you can tell what's going wrong, where, and with whom. Ha ha! Little joke from those of us who've done this. You usually can't see jack.
Under the best of all possible circumstances, your raid leader is someone who knows the fight cold, expects the same of everyone else (or is otherwise willing to explain things), and allows people time to learn from their mistakes while still holding them accountable for their performance. It's not an easy balance, and people who can do it well are notably more successful at getting their raids through content than others. You may not like being called out on doing something dumb, but there is definitely a general tolerance limit on the raid's part for wipes resulting from behavior that players can't or won't fix.
Ultimately it's a two-way street. The best raid leader in the world is still going to get a bad performance out of a raid full of indifferent or just plain bad players, and a good raid following a bad strategy winds up doing doughnuts in Black Temple's courtyard. Even if you don't raid, you want someone around who knows the 5-man content well enough to cook up a workable strategy for the group you've brought and furnish an educated guess at why something might not be working.
As my old raid leader used to observe, it could always be worse. You could be raiding for Troxed.
6. The Gladiator
"No, no, no -- you WANT that guy to blow his cooldowns, nitwit. Don't go nuts trying to prevent him from using them, just focus on surviving until he runs out of tricks. Watch how I do it."
Some of us like PvP more than others. I, personally, despise it. But that's all the more reason to make the acquaintance of someone who actually does know how how your class and spec need to be played when you're under fire. Sooner or later you will find yourself in the battlegrounds or arena if for no other reason than relatively easy access to decent gear, and no one out there is going to argue that it's a fun experience when the competition outgears and outplays you. You need someone to be the master Jedi to your clueless padawan as you struggle through the ranks -- someone who knows the tricks the other classes are likely to pull and when they'll do it, the strategy that's likely to result from the arena team composition you're facing, and whether your problems are predominately caused by your team, your gear, or your reflexes. The advice you get isn't necessarily going to be couched in the nicest terms, but someone who PvP's extensively with your class and spec can probably be counted on to prevent you from succumbing to an array of stupid deaths while you're still learning.