Sometimes I wonder how some tanks ever get to level 80 not knowing the most important tanking basics: face boss away from party/outer edge of the arena.
Get The Burn in roulette and on the first pull I notice the tank is using a Novus weapon, so I quickly mention that and they swap after the pull. Did single pulls, which was annoying, but whatever. He wasn't squishy any more so that made me a happy healer. First boss I notice they just run up to the boss and then just stand there (even in AoE's). Didn't say anything because the boss jumps around anyway. Second boss they do the same and then keep the boss' rear in the fire pool, which meant that NIN couldn't do their rear positional. Easy fix, I run to the opposite side of the arena and Rescue tank. Problem solved.
Then there's the final boss... this boss has a breath attack that's a cleave AND a tank buster. This tank kept to their playstyle of having the boss face the party, so wanting to not wipe, I Rescue them to the outer edge of the arena. Things go well for a bit, but at some point the tank suddenly had 4 vuln stacks and were now squishier than a stress ball. They also stood in the puddles and were taking unnecessary damage and then at some point the other DPS died and I just... I manage to try and salvage the run, we get past the divebomb phase and then the tank is facing the dragon inside of the arena again and the cleave is coming so I Rescue them but I was too late and end up getting myself and the NIN killed. If I did nothing, then I think only the SMN would have died (and maybe 3/4 of the arena covered in puddles, which the tank definitely would have stood in). So on second try I, again, Rescue the tank to the outer edge of the arena, but then they run back into the middle and the tank buster cleave wipes us.
Final try and we clear, but we made sure to explain to this tank that they have to face the boss to the outer edge. They do this, but in the worst way possible: they constantly ran (during the fight I asked "why are you running?"). They were a level 80 PLD, had some level 80 gear... I just don't understand how they don't know the one most important tanking rule.