Spoiler My character is a pretty nice guy. Not strictly lawful, but not one to really bother anyone that isn't asking for it. After sparing Paarthurnax, I noticed a sharp decline in the number of hostile dragons. They'd be cool with me, and only fight things like giants, mammoths, and sometimes bears. I decided I'd work to protect dragons and help them in their battles against whatever creatures they'd get in a tangle with, and I'd only fight one if it attacked me first.
One day just south of Whiterun, I noticed a dragon fighting something behind the farmstead. I ran up to it and noticed it was battling with a single guard. For some reason, without knowing for sure if this was a hostile dragon or if the guard had started it, I went up to the guard and killed him with one blow (sword-through-the-back kill cam at that, as he said one of the typical friendly-fire dialog lines).
That kinda bothered me a bit, actually, that I went and (for all intents and purposes) murdered an innocent NPC without direct provocation and without knowing who I was helping. But there was a bit of vindication as after the guard was killed, the dragon took off and didn't bother me or anyone else.