In Just Another Judgment Day, our hero is thrust up against the wrath of God incarnate in a human being, who can only lose his powers if he steps off the path of God. Even the Punk God of the Straight Razor fails to stop him (though he manages to walk away from the confrontation). How do you force the Walking Man to stop walking? stand in his way, refuse to move, and offer no resistance or any other reason to kill you. This forces him to try and kill an innocent man, which costs him his powers. And the best part? John wasn't even sure it would work.
When facing his mother Lilith, John find and wants to use the Speaking Gun. This thing is an evil weapon, that whispers in his mind, wanting him to use it further. Rather than do that, John forces it to speak its own name backwards. What's more, he takes it up again AND forces himself not to use it in Judgment Day, thus making him the only person to hold the gun more than once and turn down its dark offer.
Razor Eddie is this trope on two legs. In his first appearance, John takes him up on an owed favor to help him out on his case. Eddie does so, but doesn't charge him a favor. Instead, he makes the favor taking care of the Harrowing, the faceless humanoids with drug-syringe fingers that keep coming after John. Did we mention that he's implied to be one of the only individuals who can take them in a fair fight? And that the only time John beats them in the series, they're weakened by Merlin's magic?
Razor Eddie has also used the Speaking Gun. To redeem himself, Eddie did something unspeakably nasty on the Street of the Gods, so bad that the Gods were running out of the Street, crying, for the better part of two books. And he Took a Level in Badass while he was at it. Which is saying something.
Three men have stood face to face with the Walking Man and lived. A holy monster hunter and truly good man is one. John Taylor, a reasonably innocent man (at least, that time) was two. The third was Razor Eddie. Who fought the Walking Man to mutual exhaustion and only lost because the latter took the razor and chucked into the distance, temporarily shocking Eddie.
Suzie arguably gets one every time she gets past her trauma with John. It takes a lot of willpower to overcome the what she went through, but she does it.
For this troper, the series' definitive CMoA was all the way back in Book 2, Agents of Light and Darkness: John and Suzie are running through Time Tower Square in the middle of an angelic invasion... and there stand just four of the major league players, kicking ass and taking names as the Nightside churns to life in its own defense.
Cathy gets something of a Badass Normal CMoA in Serpent's Tooth, when John, Suzie and Eddie rescue her from kidnappers. Revived and released, she doesn't flinch or even act embarrassed by her circumstances, but immediately walks up to her captors, head-butts the woman hard enough to break her abductor's nose, then kicks the man full-force in the nuts. Suzie quips admiringly to Taylor that he's had a bad influence on Cathy.
The Oblivion brothers' mom only has one scene, but it rates as one of these because A) it turns out she's a former costumed adventurer who taught Ms. Fate everything (s)he knows, and B) she told Walker, who was being a snot about duty trumping love or family or regret, to fuck off to his face. Taylor nearly applauded.