What they said was that people who exhibit criminal behavior (especially those who were maltreated as children) have a different experience tasting coffee. I don't see any claim that drinking coffee reduces criminality.
@eurasiantiger stated that studies show that MAOA-LPR has been shown to be connected [positively?] to criminality and violent behavior. I would expect that when @eurasiantiger specifically links that to MAOA inhibitors found in coffee, that means there is a linkage between coffee inhibiting MAOA and criminality in certain genotypes.
It was simply an expansion of that particular gene variant, but yes, I would assume there is a correlation between coffee intake and impulsive crime in some genetically predisposed subpopulations, but I cannot say whether it is linear, nonlinear or perhaps inverse.
What I can definitely tell you is that there is a positive correlation between heavy coffee intake (>= 8 cups per day) and suicidality. I assume that is the result of the anxiogenic and impulsivity-increasing actions of particular Harmala alkaloids, namely harman and norharman.
Yes, but the effect on coffee drinking preferences is not limited to those engaging in crime: plenty of ”normal” people have these gene variants, and it’s likely the criminal outcomes don’t manifest at all without childhood abuse, or they manifest in non-violent ways, e.g. white-collar crime or substance abuse.
You can take any of the terms used above, even whole sentences, and enter them into Google to find further information around the subject.