I suspect the player was probably new.

Or young.

Or drunk.

Or high.

Really, though, if they were that bad, you should have vote-kicked. As you all managed to complete it without the tank's help anyway, it would have sent a palpable message that what they were doing was unacceptable.

New players often don't know things a lot, so you guys were in the right. I had one Gladiator tell me that the person who was teaching her how to tank told her to only use Rage of Halone--and not the combo. But the fact that they weren't responding to /p tells me that in addition to any greenness, they were also dumb/stubborn. If you can't accept correction, especially if you're new/learning, then you don't have any business tanking, imo.