I had to kill Valkyn Skoria in hm on my tank because all three pads were destroyed and the group couldn't survive beyond that.
Chained it to death, took me about 5 years I think. I'm talking about potato dps running to read the scroll lol
I have two experiences in that very dungeon that tops that.
First, I was with a group that could not get past the two mini boss fights just before Valkyn. To many atros has spawned before they could kill the first mini boss and we tried many different strats.
To top that off I was with a group that could not get past Urata. That bosses adds were to much for them.
I used to queue solo as a tank to help out the GF and enjoyed helping players get their first clear on a vet dungeon. But experiences like those two are why I only queue with guildmates. Can help players understand mechanics but cannot help them if they cannot figure out how to do damage.