Constantly being "offended" by something another person has done or said, frequently expressing doubts and questioning another person's real meaning, motives, or agenda, having ongoing suspicions toward another person (especially with no proof or real evidence) about betrayal, agenda, ostracizing, gossiping, triangulation, disrespect or abandonment is actually a symptom of paranoia, which may or may not a part of a Narcissistic disorder.
Having occasional doubts or suspicions is not necessarily "paranoid", it's normal human. We know from experience that people aren't always on the level, and can do crappy things, even sometimes unconsciously.
However, a person who does NOT have paranoia or a disorder is keen to find out if their suspicions are founded or not. They will often seek to find out what's true, false, or hidden. They will happily accept evidence that shows their suspicions were incorrect about a person, and will experience a feeling of relief.
If however they find out their suspicions were correct, their focus will be on protecting themselves and getting out of the mess they find themselves in, not so much on the other person; not on retaliation and revenge.
They will also often accept a genuine admission, apology, or amends, but - if they don't want to, or if there is no forthcoming apology or amends, they will simply separate themselves from the person without much ado. They won't keep the same connection with the person, nor will they make an effort to try to stay connected to the person either with positive or negative intentions.
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A person who does have paranoia or a related disorder does NOT accept evidence about their suspicions being incorrect, because that's not really their main focus. Their main focus tends to actually be a desire to feel "vindication". (This may be a loop they're stuck on from something in their past with a real person who betrayed them, abandoned them, or hurt them.)
So evidence that the other (current) person has no agenda means they have no excuse to be angry at the person, or resent them, or try to dominate them. That's not what they're looking for, so they ignore the evidence.
When they find that there is evidence to show that their suspicions WERE accurate, or even if there's a grain of truth but not entirely correct, they will typically ramp up their efforts to dominate and "punish" the person. This is what they wanted, an excuse they can use to justify their desire to go after the person whom they've targeted.
Importantly, they will ALSO OFTEN ramp up their efforts to "punish" the person WITHOUT evidence or proof of "guilt", often CREATING false stories and motives in order to "justify" their poor treatment of the person.
This behavior has been seen over and over and over throughout human history coming from "officials" who unfortunately had positions of power in spite of their mental illness; well known larger scale examples of which are the Spanish Inquisition, the Holocaust, the American "witch trials", Jesus Christ's trial and crucifixion, persecution of women in general and of certain men in many countries, persecution for religious beliefs in many countries, and slavery throughout human history.
("Persecution" is a word that describes this behavior, as well as "scapegoating", "smearing", and "oppression".)
Those who have severe paranoia (delusional) often don't really have an agenda, they actually believe their suspicions and imaginings: they're "stuck" on a feeling of suspicion of betrayal, or believing that another person is out to get them, or is trying to hurt them, regardless of any and all evidence to the contrary. (They often can be found to have been betrayed, neglected, or abused in their past as well, but they are less aware of the difference between their own thoughts and feelings, and reality.)
They may not even be aware that they are making stories up in their minds about what others are doing, and what others' motives, feelings, intentions, and thoughts are.
Those with certain disorders that may include apparent paranoia may be looking for "reasons" to validate their feelings of suspicion or resentment, or "reasons" to cast judgment and blame on the other person, or an excuse to retaliate against or ostracize a person.
It's not about what REALLY going on, that's not what they're interested in. They are focused on seeking ways to validate and justify their feelings, real or imaginary, and excuses to treat the other person poorly.
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Those with Narcissism, whether they have paranoia or not, often accuse others of "paranoia" in order to paint them as exaggerators or liars. They are not that difficult to spot because they don't have compassion for the person in mind when they say it; in other words they are not stating an observation about the person's health, and having concern for the person, which a non-narcissist would have if they realized another person was displaying signs of mental illness, actual "paranoia".
(Using a mental illness as an accusation, like the person is "bad" for having it, or as if the person CAN "help it" but refuses to, as if they're "using it" as a way to get attention or an easy life, is a common Narcissist behavior. I have personally witnessed this numerous times coming from family members of autistic people, friends and acquaintances of those with mental, emotional, or neurological issues such as anxiety, depression, bipolar, bpd, PTSD or OCD, and from PAID "caregivers" of mentally disabled children and adults. ~ If you can imagine an adult person saying "he exaggerates his Down Syndrome issues in order to get attention, just ignore him.")
Paranoia Disorder