Tried to heal a Naxx25 run for fun.
It wasn't fun.
Seems the only thing everyone else knew was what the achievements were for each boss. Not the mechanics of the fights or even how to execute said achievements, just the wording of the achievements.
First Quarter is the Arachnid. On Anub'Rekhan, tank runs ahead while some adds are beating on ppl's faces in the previous room. I backtrack and help them, and the tank pulls the boss, locking the three of us out. Tank dies, but the dps kill him easy enough. Finish the Quarter with minimal stupidness and netting all the respective achievements for that section.
Next we do Plague Quarter. Noth goes fine (not much to screw up there), but Heigan is a different story. We fail Safety Dance because the tank taunts Heigan down off his platform right at the start, and the alternating green takes out 2 ppl. Finish him off, move on to Loatheb. Fail Spore Loser obviously, so we just finish out the Quarter.
Lastly (I say this for a reason, you'll see), we go Construct. The green river's lethalness is lost on most of the raid. On Patchwerk, tank pulls him, IN THE MIDDLE OF THE SLIMES. Needless to say, everyone goes down, and I make for the exit like a madwoman. Naturally, most of the raid fails at getting back to the instance (Venomspite is sooooooo far away from Naxx, apparently). I run back in, mass rez, meticulously explain how the fight SHOULD be pulled off, and we kill him. We kill the adds in Grobbulus' room, followed by ol' Grobb himself.
The pipe. OH GOD the pipe. Before I even have a chance to explain, they're already on the other end. Boss doesn't pull, but some fell down through the holes and aggro some out-of-the-way adds. LOS issues, and they die. I jump down and rez, and we run back around. This time I explain how leaving the very end of the pipe and entering Gluth's room instantly makes him aggro, as well as the Zombie Chow mechanic to the fight. I lead them down the pipe, and wouldn't you know it, someone autoruns out of the pipe. We jump down and lay into him.
Except he doesn't die. Gluth repeatedly eats zombies, and his health is a roller coaster nightmare. I just had enough, so I healed the best I could, and when there was only a few left, I hit Fade and Hearthed. I didn't want to be a b!tch, but I also didn't want to go through this painful drudge through Thaddius and his achievements, as well as the Military Quarter and Sapphiron & Kel'thuzad. None of them (or so it seemed) had ever been there before, and assumed it would be a faceroll at our ilvl. Which isn't a stretch, but when I have the most health of anyone, then there's a problem. If you want to be helpful, then at least make an effort. Don't expect everything to be so easy.