Also agree this would be a fantastic idea, I've met some really friendly people in dungeons, but sadly also not so friendly
Doing DF low level roulette other day got ifrit, and healer would not stop going on about how we will fail because one person in the party was new and how they should get FC to boost them through content not expect strangers too..
I snapped back to which healer said they wouldn't heal me for defending the person.
We nearly wiped due to the new one not knowing about the nail but I politely explained it whilst trying to solo down, they then switched and helped kill.
I was honestly shocked by their attitude it was ifrit story not extreme, why shouldn't a player playing it for the first time be able to do it .
That was definate a case of I wish their was a DF blacklist so you can make sure never to team with them again and as pointed out might help in some peoples attitude if they realise being a douche will have long term effects in how quickly they get a run