Fe and te, for their respective users, affect the lens that person sees the world. xNFJs and xNTJS have the potential to have similarities and see eye to eye but that is where the dividing point begins imo. Many times, when people who fall under one of these types don't really have good experience with the other, it's the fe vs. te divide that's the culprit. Te usually focuses on logic more and is more blunt, caring about structure so users will not be afraid to put their foot down. I can see a sharp tongue if boundaries are intruded. With fe, there's a certain coldness that can come with the dark side of fe.
From my experience, we want to understand people, and a certain anxiety can come with fe reading into the emotional environment. But if our boundaries are overstepped or there is conflict with a person, the instinct is to push the person away. A fe auxillary might keep thoughts like this internalized and need time to process. If we were nothing but polite to that person, it may come as even more of a shock than what te can do. With te, you usually see the harshness coming but with fe, it builds up the and the person on the receiving end doesn't see it coming. I've been on the inflicting end mostly but there have been a few instances where I've been on the receiving end and not fun. xD