Dear Blessings,
There are always going to be people like that literally everywhere you go from family reunions to flying on an airplane and the person sitting next to you. The reality of life, everybody only cares about themselves vs. any concern for your challenges and are compelled to express them in any way possible. You may be right and this expression of one-upmanship is a sickness in itself.
However, I am more concerned about you than the others you mention. I understand how this behavior is cumulative to the point now you see and look for that behavior within A, B, and C. These are all "little people" with "little minds" and divisive behaviors. When faced with these types of people in this type of situation we must not give them permission to hold power over our lives eating up precious energy with negative feelings and emotions. It is our choice to allow them that power or not. We get to a point we "know" what these people are going to do and we actually look for that behavior. What happens when we look for something like that? We normally find it (or it finds us) one way or the other. Once we again find that behavior it only aggravates us even more because now we say to ourselves, "See, I told you this would happen," and the cycle starts all over again.
These are the types of "toxic people" who suck the life out of us. We don't have a whole lot of extra life to devote to this type of behavior and removing the cause may initially be painful, in the long run it is a major improvement. I understand all of the above sounds very hard in itself but since we can't do the alternative, what choice is there for our own sanity? Oh! The alternative? Take them out and shoot them.
In my case I no longer engage with people of this type and have removed toxic people from my life. Although, I can say something to them you can't and there is no way they can one-upmanship me on it. I flat our tell them I'm terminal and that seems to work every time.
I really have no answers for you, but do fully understand how you feel and feel for you at the same time. I apologize for running on about this but thank you for putting up with me for this long.
Peace be with you Blessings. You are NOT alone.