I still have yet to experience the toxic endgame community but I have basically level pld to 50 in DF and warrior to 38 and have only experienced a toxic player once. If it is my first time in the dungeon then I let everyone know, if they don't like it then they can wait 45 minutes in the queue for a different tank. I am also a solid tank and have dual monitor setup so I always have boss strats up on second monitor for new encounters.
The best advice I can give to tanks is to level other classes and learn their mechanics so you have a better understanding of what to do when grouped with certain classes, what is getting cast on you and the enemy (e.g. buffs/debuffs), their CDs and traits and what level they get things, etc. With BLM I expect sleept targets, with SMN I expect to flash more often because of Bane, etc.