Funny story. I had a healer in Vault once, dressed in Ironworks gear, who got angry with me for pulling the hall after the first boss. I told them that I haven't noticed that they were so undergeared... you wouldn't believe how much offended they got. I almost felt like it was my fault for their lack of gearing up.

The question is where is the line? Where is the line between playing badly in acceptable way and playing badly in unacceptable way.

Somebody playing poorly might be acceptable for one player, while totally inexcuseable for another.

I would say put in at least as much effort as your tank and healer.