I want to confirm what this person said.
When I started the game, people where friendly in the low-level dungeons. I just said "Hi, I'm new here. Any tips?", they were patient. Same thing when my GF started playing, but she went as a Tank job - people where cool with it too.
In the max lvl, my experiences changed a little bit. Patience is still here, but sometimes you'll get the weirdo who rushes the dungeon before gauging the other 3 members. But, even with impatience, they've mostly been gentle, with maybe a little touch of weirdness when they queue as groups and start laughing at internal jokes.
...In comparsion, I re-subbed to WoW for 6.2, and couldn't do Iron Docks without some crazy crackpot calling everyone trash or that awful Paladin in LFR telling everyone that he was carrying "this shit group" and we didn't deserve his help. Ugh.