So I Recently Picked up WAR

[Kenky]

"The tank refused to tank."

Not failed to tank. Refused. In order to grief specific individuals to the detriment of the group as a whole. Which is what you were just suggesting.

Incorrect.

The tank could already be dealing with other mobs, or are personally uncomfortable with pulling more than they can handle. The DPS running off and pulling more is not "The tank refuses to tank". It's the DPS being a prick.

Communication. The easiest way around this is to say, before pulling anything, is that you're new to tanking and will be pulling small until you get some confidence. If people have issue with that, then they can leave and find a new party. This is also something that Healers can do, by asking the Tank if they intend to pull big/small. Forcing players to take more than they are comfortable with is the punishable part.

And lastly, accepting their stance and moving on. People don't jump into the tank role and immediately go wall-to-wall and survive. People don't pick up White Mage and suddenly become impossible to kill. We all start in the novice side of the spectrum.

Edit: An extra caveat is simple. The DPS running off ahead to pull more than the tank? That is the DPS trying to force a Speedrun and that is punishable by the ToS. It is not the Tanks failing / refusing to do their job. The DPS in that scenario cannot report the Tank, even if the Tank decides to "let the DPS die" (which is technically a fault on the HEALERS part, not the TANKS part.)