A couple of years ago, in the 50th anniversary special "The Day of The Doctor" we learned that The Doctor chose his name "Doctor" because of a promise:
Clara: You told me the name you chose was a promise. What was that Promise?
Tenth Doctor: Never cruel or cowardly.
War Doctor: Never give up. Never give in.
In fact, before this story, the War Doctor wasn't considered worthy of the name "Doctor" because, as Eleven said, "He's the one who broke the promise" (In "The Name of the Doctor").
In the series 9 finale "Hell Bent" we see The Doctor...
Break every promise and rule he's ever lived by just to save Clara. He banishes Rassilon and the High Council from Gallifrey. He shoots the General in cold blood (sure, he/she regenerated, but still). That seems cruel to me.
However, I can think of another instance in which The Doctor broke that promise. I'm talking about the Tenth Doctor's story "Human Nature" / "The Family of Blood":
Son of Mine: He never raised his voice. That was the worst thing— the fury of the Time Lord. And then we discovered why — why this Doctor, who had fought with gods and demons, why he had run away from us and hidden. He was being kind. He wrapped my father in unbreakable chains forged in the heart of a dwarf star. He tricked my mother into the event horizon of a collapsing galaxy to be imprisoned there, forever. He still visits my sister once a year, every year. I wonder if one day he might forgive her, but there she is. Can you see? He trapped her inside a mirror. Every mirror. If ever you look at your reflection and see something move behind you just for a second, that's her. That's always her. As for me, I was suspended in time and the Doctor put me to work standing over the fields of England, as their protector. We wanted to live forever. So the Doctor made sure we did.
I mean, The Doctor literally unleashed hell on them. Doesn't that count as being cruel, and hence breaking his promise?
Are there other examples of The Doctor breaking this promise? Particularly in Classic Who, which is hard to me to find episodes of. For reviews I've read, the Sixth Doctor was kind of a jerk sometimes.