I find that in many cases you have to go along to get along. People tend to find it easier to ignore or attack than debate. Sometimes carrying the disagreement into other topics.
Important thing is how long you let it bother you. I don't stay angry with most people long. I'Il get upset then try to get along Again, sometimes apologize even if I'm not the only one that caused the disagreement., at times it works, sometimes it doesn't.
The boss would have the upper hand in that situation, I would think, "maybe". I agree it may need some additional attention, because of what they may do. Some people are revengeful and it could be dangerous. I think some people have a loose screw or something, from what they do sometimes. For "example". I have this neighbor, who speaks sometimes and other times will look right at you wave at him, and not speak, just giving you a hateful look. The other day at our fence he comes up talking acting like everything is fine, just talking away.
To answer the thread title question, "When You Unsure Why Someone Doesn't Like You, How Do You Deal With It?", I quote the standard Jersey response, "Forget about it." They have their reasons and I don't care what they are. I don't live my life to please others.
A former female colleague didn't like me, I could tell by the funny look she gave me when she first started, I just avoided her and only spoke if I had to, she left a few weeks ago and apparently she didn't like any of us and her attitude was just awful.
It just occurred to me that if someone did not like me and I was unsure as to the reason, I would give them a reason to dislike me so the ambiguity would be removed from my life.