But, it's normal to them. And in the US, we don't really get to tell other people what to consider normal - we just have laws. I guess you'd be surprised about what people say about slap fights and this kind of violence - it's very common and to many people who live it, is normal. Of course you can judge, but you won't understand them if you don't realize that their threshold for what's abnormal is different to yours.
Further, I have an entire database of crimes (mostly murders, all kinds) in which the main thing that people who are not residing with the perp will say is, "But he was so nice, we never would have thought this."
I got interested in this topic when I was 17 and the boy who lived behind us (a sweet, quiet boy who was a bit of a loner, but we girls found him sweet, not particularly cool, kind of cute, a little awkward)...got up one morning and shot both of his parents. I suppose it could just be the neighborhood, but 30 years later, a man who was everybody's friend and aged about 60, shot his brother and killed himself. That was in the house across the street from the boy. Both families were "normal."
If there's one thing I've learned from a life of academic study of crime, it's that there's always a story, and that "quiet, nice kid next door" often isn't, if you go and interview siblings (I think CL almost said something about it) or parents...
I doubt Gabby's parents knew he had taken her driver's license, or that they specifically fought over phones, or that he hated "infestations" of people in nature settings, or that he had severe insomnia or "episodes" in which he thought he might be hearing voices or hallucinating (per MSM from Gabby's friend). They may not have read that, even now. I would wager that neither parent was familiar with his social media and, like most parents, probably wouldn't have been able to interpret it without the context of his entire behavior - and seeing his natal family dynamics up close.
But his parents knew him. There's a reason he was still living at home, underemployed, dreaming and painting and drawing cartoons, reading scifi and thrillers, creating music playlists - these are not employable skills. These are occupational therapy, IMO. Gabby joined his team of helpers.
I doubt that Wayne Couzen's fellow employees had a clue about him. People with deep issues find ways to conceal them, especially with help from families. However, their "fixes" are jerry-rigged and highly subject to falling apart under stress. They know how to duck and cover, as we are seeing in this case.
I learned all that from LE. And then I learned it from law professors and psychiatrists. And in hospitals for the criminally insane. And in VA hospitals, where people were in locked wards for running amuck. Often, their comrades and commanding officers were shocked ("Never thought he was the type"). But the psychiatrists and other researchers concluded differently. The clues were there, but a person might need training to see them. And the stressors were obvious too. Even though the patients were hopeful that they could "buck up" and be part of society, they could not.
I think many, many people survive relationships like the one Gabby had with Brian (in terms of the degree of spatting and face smooshing and girl slapping) and did not kill each other. I'm not condoning slapping and pinching, of course (and I would tell my daughters to leave), but in real life, most people look the other way when young people have what they feel are "minor" issues with interpersonal boundaries. Everyone figures they'll learn. But in certain conditions involving deep-seated issues, the behaviors escalate - often suddenly, and I do believe that sometimes we can suss that out before it happens.
The question is - what is different about BL? I refuse to think it's just some random neuron misfiring (unless drugs are involved, which I do not think is true) or that there were really no signs at all - but the signs weren't apparent to young Gabby and probably were more complex than just his behavior toward Gabby. I also think Gabby saw a parent-structured version of Brian. As most people do not feel completely themselves while living with their parents, Brian had not had a chance to figure himself out, out in the big world. The structure of Brian's world had changed a few times, in the two years before this incident, and his previous coping skills (gained to help with his issues) were not sufficient to this next phase of life.
At all.