If you want to experience a lie, try this phrase on for size:
"I don't think X likes me"

Even if these truths are self evident. Even if X snears or calls you a bitch or never looks you in the eye. Even if it is beyond obvious that X  would choose a nonstop elevator ride for hours straight over cocktails with you, the person hearing this statement will argue. I promise,
"oh no, I am sure you are mistaken"
"oh, they are just shy"
"or, I think they are just intimidated"
"you are so paranoid!"

I have learned, mostly to keep these thoughts to myself. Sometimes I make the mistake of telling my husband, or a close friend, but mostly I have learned my lesson: we are supposed to pretend that those that don't like us actually do.

I find this ludicrous. Not everyone likes everyone and most people dislike at least one or two people. I know I do.
I do understand that enlightened, mentally healthy people may be able to relagate those they find grating or frustrating or offensive to a gray zone of tolerance.  And perhaps, yes, those people may very well be the exception. Maybe they dislike no one.
But even so, they may not, despite seeing your value as a human, actually LIKE you, or like me, or like her.

That seems pretty much OKAY to me.

But even weirder than the intense discomfort people feel when you approach them with the reality that someone you interact with may find objection to you, is the belief that convincing you otherwise will help you relax, put you at peace.

It is like telling someone a hideous picture of them is great. I mean, if they look like a gargoyle in this picture, and you tell them it is a wonderful likeness full of sunshine and kittens...how are they expected to feel? They can see the picture. They can see the issue infront of them. Are they then to believe that they look like this, that this is  their good side? Are they to question their judgement when there is no reason to? It is silly, just admit there could have been better likeness and move along.

Likewise, trying to convince ourselves someone likes us when they clearly do not, whether the aversion is overt or simply in the form of energetic non verbal cues, just creates a new discomfort, a new cognitive dissonance apt to create more opportunities for unpleasant interaction and delusion.

Finally, I think for most people, accepting that that someone holds them in disfavor can be an empowering, potentially educational moment. I know when I ponder the reality that someone that I have not evidently gravely offended dislikes me I am usually on the verge of asking other questions: why is this? should I do something about this? should I do something about me? do I even like them?
These are all relevant questions, opportunities to explore character growth, fodder for consideration of you wish to engender and grow intimate with, who you are willing to let go.

So practice these phrases, should you presented with an opportunity to supply such falsehoods

"well, they don't like many people"
"what makes you think that?"
"does this bother you?"
"well, good thing *I* like you"

People expressing disatisfaction are sometimes looking to unload, but sometimes they are also looking to start a constructive dialogue. And you can't pretend unpleasant realities don't exist because you don't enjoy them. I mean, if you look away from the Sun you'll see your shadow. And maybe you will see them, behind you, giving you bunny ears. Or maybe even the finger.