I think cops have been given far too much deference for self-defense. I don't buy that this cop had any reason to worry about his safety in this stop, and you're just offering it as a default catch-all defense.
Sure. And if only people were just nice and polite to each other, the world would be a friendlier place. But the fact that she didn't doesn't constitute a crime.
I don't necessarily disagree that requesting her put out the cigarette was reasonable. But it isn't illegal to refuse a request, and it certainly isn't grounds for an arrest. He could have handed over the warning and let her go on her way, but because his ego was bruised, he didn't do that. He escalated the situation, when he was in the position of power, and while her actions were potentially rude, his actions were unprofessional, likely illegal, and irresponsible for someone who is employed to keep the peace, not fight a personal battle.