Tank should be able to keep aggro. DPS should be using aggro mitigators on bosses, but that's as far as you need to go. If the tank can't hold aggro after you have used all the tools at your disposal to manage your aggro, no one else is to blame except the tank. In tanking stance, a simple 123 is enough to hold aggro against even competent DPS. Not holding aggro means that the tank wasn't even doing that much.

I would suggest initiating a vote-kick in a situation like that. People that obviously don't know shit and still berate others are the worst.