Just getting straight to the point, having leveled multiple tanks, and a heal or two I feel I can speak on the matter factually and be somewhat clued in on the situation.
Here's the issues - as a leveling character, you WILL be rolling on tank/heal items together with dps who claim it's for their off-spec. Now, let's forget for a second that you either ask and/or have the greed option for offspec rolling, YOU WILL NOT play your offspec for significant amount of time, let alone, be able to build a set for it during the leveling period as you will keep outgearing most of your pieces as you go along. You want tank/heal gear, roll a tank/heal or pass on the loot.
Why is this your fault? The normalization of the situation. Rest of the group just wants to carry on and finish the dungeon without hassle. Why not? It's not them who just got shafted, they couldn't give a toss.
What should you do instead? Boot the mothertrucker who ninjad the gear, or at THE VERY LEAST do not press no, when the tank/heal initiate the kick for a very valid reason. If they needed on one, they will need on the rest.
Next, the constant ability vomiting. No, Mocking Blow is not a dpsing ability. No, you shouldn't death grip, as it saves you time running up to the mob. Your pet's taunt does not do damage.
Again, same issue and ability to resolve it. Why are we oblivious to the fact, that tank is struggling to keep a pack of mobs together? A healer is burning through mana as fast as a fat kid through gatorade? Finish the pack, have a word, repeat offence results in a kick. STOP REFUSING THE KICK OF A TOSSER WHO IS PULLING IN THE DIFFERENT DIRECTION THAN THE REST OF THE GROUP.
I've got heirloom geared characters, once in decent level, I will have dungeons running as a clockwork, but regardless of how fast or efficient you are, there is always someone pressed for time, wanting to go faster, willing the pull the extra pack, sometimes even disregarding the fact, that your group has almost no AoE capabilities.
Long story short - START SUPPORTING YOUR TANKS/HEALS. If another dps takes a piece of their gear, don't sit silently and initiate the resolution, be on tanks/healers side. Initiate the kick if you have to. Be ready to carry on 4 man until you find a replacement if you have to, even if it means going slower. Don't prioritize finishing the dungeon over what's right, otherwise it might simply mean you won't see that tank/heal ever again.
Rant over.