Cross realm dungeon finder systems always lend themselves to trolls and toxic players. I played WoW a long time ago before the dungeon finder, and I have to say that the community back then was a whole lot better. You had to form groups, you had to find people on your own server to run with. Because of this, people's friend lists were brimming with people they enjoyed playing with. They took the time and effort to find these people, and friendships were built and the dungeon experience was a much more pleasant one. If someone was a total jerk, they got removed from the party, we found someone to replace them, and we continued on. I have to honestly say that it was VERY rare for anyone to explode or go insane back then, because they knew if they did, they'd be alienating one more group of people that they needed if they wanted to do the content.
Enter random dungeon finder! The bullies, trolls, and general jerks now have a way to get groups! They don't need to make friends! They can just repeatedly subject some poor group of random sods to their bad behavior. On the few days when they decide to keep their mouths shut, they might not alert people to their noobish ways. The bad thing in FFXIV is it does not have a crossrealm blacklist, WoW does. In WoW at least, if you get a total jerk in your random dungeon you can put them on your ignore list and never have to group with that character again.
It's sad that there are so many trolls and jerks on the internet, and MMOs need to stop giving them ways to have access to an infinite number of people to troll. We need a smarter duty finder that tries to first pair you with people on your own server, and then fills the remaining slots with people not on your server. We also really need a crossrealm blacklist so that if someone is mean enough to you, you can just put them on your blacklist. Also, blacklists need to be account wide. If you ignore one character on someone's account, even if they make an alt, you really don't want to hear from that alt either.
I feel, the best policy is to be kind and polite to people as much as you can! Make friends on your own server in LS and FC and just in general. The more on your friends list, the more people you might have to group with. Even bringing one friend into duty finder with you reduces your chances of getting a random troll. When you end up in a completely random group, speak up first, tell everyone hello, try and set the mood with a friendly greeting. If people are still jerks from the start, then it just can't be helped.
The thing I try to do is keep in mind that the duty finder is a new system in a new MMO and that they will work to improve it as time goes on. It was the same with WoW. When the dungeon finder was first added, there were a whole lot of necessary features that it was lacking. We can just post our ideas and hope that the devs sit up and take notice. In time, it will get better, and until then, the best thing anyone can do is make lots of friends on your own server to try and fill out some of those slots that were always random before. If you can't be bothered to make any friends at all on your own server, you don't want friends, and you don't want the social aspect of a Linkshell or FC... then you just might be part of the problem!