You pull it, you tank it is griefing / obstructive gameplay. It is a plain example of someone going out of their way to undermine a dungeon run just to 'punish' someone, typically at the direct expense of the other 2 or 6 people in the party who are totally uninvolved.

Report people who engage in this kind of behavior without a second thought, they can and will be punished. The majority of people in the community (at least towards endgame) think these types of players are mentally and emotionally stunted.