I wonder if this is the case of IxIs, perhaps maybe xIEs. A lot of INxps seem super calm and phlegmatic on the surface, even have this really soft and dreamy look, they almost seem like they could break if you raise your voice at them, but when I you manage to hit a nerve they explode like crazy with all the yelling, screaming, breaking things with very poor self control. Maybe Fe can even exaggerate this reaction making them seem almost insane.
I'm not talking about public bursts of anger, rather the subtle kinds that happen at home or with very close people. Like their coworkers know the xEIs as the peace loving butterflies but if their husband happen to strike a nerve at home they become aggressive. Also not talking about actual violence, more like they become that kind of a person you really don't want to argue with because their emotions and anger just get out of hand easily.