From TV Tropes' entry defining the Tautological Templar...
Considering all the puppy-kicking and Moral Event Horizons the Knight Templar gets into, sooner or later a(nother) good character is going to get the courage to ask them something. How on earth do they believe themselves to be "absolutely good", given just how spiteful and needlessly cruel they are?
The Knight Templar's answer is simple. They are good, and their every action is good because they are good.
Or, to break down the argument.
- I am good.
- Any action that a good person does must also be good.
Conclusion. Any action I do must be good.
Obviously this argument seems wrong. But I have a hard time knowing if the argument is wrong because the premises are wrong, or if the argument is wrong because it is using a logical fallacy (such as a "circular reasoning").