Meanwhile, Murdoch said, quietly but audibly, "If you want to hurt somebody, you can hurt me. Go on. Hit me. I won't hit back. You can do it until you're not angry anymore. I'll let you." (1.24)
Murdoch is a pretty impressive dude. When Matthew first sees him, he's challenging an abusive dad to hit him instead of the kid. It's the kind of first meeting that leaves a strong impression.
She had the big kitchen knife, and it was pressed to my throat. And as she laughed, I could feel it shake in her hands, and push against my skin.
She cut me that night. Just a little.
Just to teach me not to steal, and not to sneak. (2.5-7)
Nikki isn't just violent, she's also unpredictable. How could Matthew have known that she'd come after him with a knife just for taking an Oreo? That's just over-the-top and ridiculous.
She snatched the plastic bag of mussels off the counter and slammed me across the face with it. Once. Twice. (7.30)
The Walsh kids are used to Nikki freaking out and assaulting them at any moment. Matthew isn't even that surprised when she goes from happily planning dinner to slamming a bag of mussels across his face within seconds. That's just Nikki.
Emmy, there was no possible way to protect you from hearing that our mother had hooked up with and seduced a stranger, a large man, intending to get him to do physical harm to her ex-boyfriend. (24.5)
Well, this is awkward. Nikki will do anything in order to get her way. When she wants Murdoch hurt, she'll even seduce a bunch of men to convince them to go and beat him up.
I couldn't stand her fiddling around anymore. "Aunt Bobbie told me," I said to my sisters tensely, "that Murdoch beat Mom up today."
"Good," you interrupted fiercely. (27.14-15)
There's no lost love between Emmy and her mother. When Aunt Bobbie comes over and says that Nikki has claimed that Murdoch beat her up, Emmy isn't even worried about her. Instead, she's fully on Team Murdoch.
She called me into her apartment one evening to tell me that Murdoch had gone to the emergency room the previous night. "He'll be fine," she said. "He just—well, someone bit him." (37.3)
Who in the world is Nikki dating these days—Edward from the Twilightseries? Somehow, she's managed to find human men—not vampires—who are willing to stalk Murdoch and bite him. Yes, bite him.
The other person was Julie Lindemann, Murdoch's next-door neighbor. Julie had been seriously hurt. She was going to live, but that was a miracle, because, among other injuries, her neck was broken. (38.8)
Nikki leaves so much collateral damage in her wake, and she doesn't even feel sorry. An innocent woman has been paralyzed because of Nikki's recklessness, and all she wants to do is get her revenge on Murdoch.
And Nikki attacked. She threw herself at my back, hanging on me with one arm while she clawed at my face with the other. Pain ripped through my cheek. Her weight was heavy on my back. I felt one of her legs twist up as she tried to kick me in the groin with her heel. (44.25)
Apparently, going to jail a couple times has taught Nikki absolutely nothing. Instead of making amends, she goes right for the jugular and physically attacks Matthew the first time that she sees him.
Then some survival force in me took over. I reached up and grabbed her arms, and managed to duck. To my surprise, she flipped over my head and landed with a thump on her back on the carpet in front of me. (44.27)
Up until now, Matthew has always just been a passive victim of Nikki's crazed violence. But enough is enough. At some point, he snaps and pushes her back… if only to get away from her as quickly as possible.
I was filled with open hate for Nikki now. I daydreamed about picking her up and sending her flying, headfirst, through the glass and boards of her own front window, to land in a pile of broken bones and bleeding flesh on the street below. (45.15)
Dealing with Nikki's awfulness has taken its toll on Matthew. Instead of feeling forgiving and loving toward his mother, he's starting to fantasize about doing some very violent things to her. Can you blame him?