I had an unhinged coworker. Always talked about his guns. Shouting matches with the boss. Storming in and out for smoke breaks. Impotent rage expressed by slamming stuff. The whole works.
Once a week, I bought him a mocha espresso, his fave. Delivered with a genuine smile.
My hope was that when he finally popped, he'd spare me.
Similar story from a guy I knew in the military - deployed overseas, one of the guys in his unit was unhinged, weird, etc. Sounded kind of like a black sheep, but my friend always went out of his way to be nice to him. The other soldiers asked my friend "why are you so nice to so-and-so, he's so weird he's probably gonna shoot us all up one day" and my friend replied "exactly".