A similar experience happened a few days ago. I was on my i96 white mage doing the low level roulette. Well, I ended up with Toto Rak (for the third day in a row, but I digress). There was the tank who was maybe level 40, a black mage in the mid 30's, and an archer who had never been to that particular dungeon, and I'm guessing was around level 28-29.

Well, tank states he wants a speed run (of Toto Rak, I know right), so ok. We "speed run" the whole thing and get to the final boss room. We're standing there waiting for the archer (who was new to the dungeon) to watch her cut scene.

Well, the black mage decides to jump down to the boss area, which as you know, sucks everyone in, starting the dungeon. The poor archer was stuck outside locked out. She had a measly 30 seconds left of the cut scene.

I said, "really?" The black mage responds "yes, really." We finish, and the archer stated she was new and watching the cut scene. They locked her out from attempting the boss to save 30 damn seconds of their precious time. I told them it was rude of them to do that, and the response I got in defending the archer was to "quit crying." Unvelievable.