General Rule of thumb: when you Duty finder you will find one of two types of people in EVERY group.

1. The new people that have no clue what is going on and either suck or need explainations for everything.
2. The elitist jerks that do everything better than you - so you MUST listen to them when they tell you how to do your job better than you. (Warning!: these people are usually highly sensitive and insecure with their play and will do everything in their power to ruin your dungeon when you talk back to them.)

Either be prepared to put up with these people or only go into dungeons with a group of friends so you don't have to deal with it. Don't cry on the forums about how your dungeon group isn't some perfect 4 player party that executes every pull perfectly with ease lol.