A lot of times we think less of ourselves than what others think of us. And that's the situation my character is in right now. He thinks people don't respect him because he's a big "nothing" but the reality is that most do at least respect him at best, and just think nothing of him at worse. The issue is showing the events. Obviously, if they don't actually have any negative thought towards him, they're not going to disrespect him. But he thinks they don't think highly of him and he needs all these outward things to show that he's worthy of respect. How do you show that. I know this is real. I've been watching a lot of shows about spendaholics who feel they must have outward appearances to belong.
Have you ever been late to a meeting with friends at a restaurant? When you entered, I bet you found your friends clustered around each other, and you had to take the spare chair. This situation—not being included—was your own fault (because you were late), but despite knowing that they just did what you would also have done, had one of the others been late, I bet it felt a little bit weird and sad. This is just one example of a situation where the actual situation can get misinterpreted. Tie a string of them to each other, put the emphasis on the perceived wrongness but inject just enough doubt that I don't think your MC an entitled prick.
To give an example from work this morning: the context is I'm leaving my school for a new one to work there as a teacher. Last Friday I went to my new job for orientation and to meet my new class. I went back to my old job this morning (because I have another week there) - not one of my team asked me how it was I'm leaving on good terms, and everyone's aware I'm leaving - it's not a secret. My team knew the purpose of my taking Friday off. You'd think someone would ask, just to see how it went, even if for curiosity's sake? Then whenever these same colleagues have discussions about the class - which I assist in - if I make a comment, everyone simply pauses to give me space to speak, because they're polite, and then they go right back to their discussion as though I'd never spoken. There's also no eye contact. The worst thing you can do to a person is ignore their existence. It need not be outright hostility. Indifference hurts more. It shows you have no value in their eyes. It shows you're not even part of their group to begin with - the message is: You don't belong here, and your skills and opinions are neither wanted nor needed here. Yes, I'm glad I'm leaving
I'm a pretty weird guy but I have a tendency to always listen, but inability to feel true to myself asking questions (too many 'caring' ones drained me early on in life) with answers I'd expect my friends/acquaintances to simply divulge without being prompted. I expect them to know I already care. It can be derivative of depression/personality traits sometimes. Perhaps you're moving into a superior role and they don't like that? So many interactions in this world are just objective... Sorry, realise this was a bit of a derail.
If your character has friends or close acquaintances who do show him respect, and that he matters to them, you can always have your character (via internal thoughts or through the exposition) think the following: He knows his friend cares, knows that this friend genuinely doesn't think of him negetavely, and yet in his heart he feels his friend has no right to be so kind and lenient. He doesn't deserve their affection. Now, I know this isn't exactly about respect, as you mention in your original post, but it's the kind of psychology I'm sure is still at play. I myself have a lot of insecurities, such as feeling I am too young, petite, and innocent to be taken seriously by the more mature friends and coworkers I have. And growing up with insecurities is I guess one reason why writing such a flawed character as the MC in my current story is kinda easy. It's not apples to apples, of course. I never want to copy-paste my issues onto one of my own fictional characters. But it helps make it easier to understand the character's psychology. I know it's irrational; my character knows it, too. But that's the point. We humans are own worst enemies and find fault in ourselves for every critique or even kind smile from people around us.
One way to do this, at least with the people who dont really think about your character at all is to take a relatively normal situation, something like an office interaction, and make it more then it really was. Maybe the coworker needs some numbers from the Main and asks for them but the main character sees this as the guy doesn't think he does his Job well. Turn something simple into something more then it really is to show what your character thinks of themselves. Hope that helps.
You could get ideas from your experience with an insecure person. I know several people who have personal insecurities. For a long time, I hadn't noticed their odd actions as signs. That was until I got to know them better. I wouldn't say that this is the case for every insecure person, but it's common with the ones I know of: they hide their insecurities by pretending, but sometimes they end up exaggerating. Sometimes it gets to the point that makes them seem condescending. They tense up if they think something about themselves that they're embarrassed about might get revealed. And they tend to be loud about it. I'll give you an example. I have a cousin who annoys his friends because he can get condescending. And he pretends to know it all. He can be a bully, too. I used to be baffled until I started to know more about him. His mother gave me his encyclopedias when he was studying abroad. I found his old report card that was hidden inside one of the books. He failed every course at that time. Later on, I learned that he got kicked out of the university. He got accepted back a few years later after writing a letter. I know this because his mother and my mother are close, and his mother expresses her personal worries to us. My cousin isn't aware of this. I began to understand him, and it helped me get along with him better, although I don't meet him as much as I used to. I have another cousin with the same issue except she doesn't bully. And she's embarrassed about the things that are different from the other cousin.
I just want to point out: This is called having an inferiority complex. He misinterprets - willingly, albeit subconsciously. He makes excuses. He rationalizes. "They're just saying that to be polite, it's just pity, they don't really mean it." Etc. Ultimately, you're dealing with a character who refuses to trust in whatever positive opinions others have of him because they simply don't match the way he views himself. Any praise and appreciation clashes with his sense of identity, and the human mind interprets this as an attack on it's integrity. It will conjure up whatever lies and delusions it needs to protect itself.
Alright, so you're not looking for an explanation of the phenomenon but rather ways to express this through writing technique. Lemme see.... - internal dialogue. Clumsy, I know, but doing it a couple of times can work. Like, have an action happen, and then have the character have a totally negative opinion of it. Like someone says they ran out of something he wanted to buy at the shop, and he thinks that the female worker is one of those snobby girls who thinks he would look stupid if he wore/used whatever he wanted to buy. - random thoughts. Like, something is going on, and the character just has a random depressive thought about how dumb or weird they are. One time I had a strange moment at a church event where I thought I had a weird name (even though my name is fairly common and even in the Bible) and that I'm weird and no one will ever like me. Nothing provoked it, and no one was even paying attention to me at the time. - Have an action happen, and then have someone ask the MC about it, so that he can give a skewed interpretation of events. - Set up the MC's expectations that something should happen at a social event that means people respect him, but in fact is just some simple gesture that means nothing in particular. Like for example, let's there's a mascot at a local event, and it's a tradition to take a selfie with a good friend and a mascot. Since no one takes a selfie with him, he thinks they don't like him. (Sorry about the silliness of the example. That's the first thing that came to mind.) Or maybe the friend group is sharing food, and the run out before MC gets any. I dunno. Ooh, okay, here's one that makes sense. So they're doing performances at school or wherever, and when he does his, he gets polite applause, but someone else gets cheered enthusiastically. - Show him being too uncertain to want to talk to people socializing. - Have someone laugh at the movie he wants to see. That's all I got. Edit: Oh yeah, one more thing. Have MC criticize anything he does, even without hearing negative things from others first. Like, "I made this sweater. It kinda sucks and the colors don't work, but I'm still proud I actually finished something for once."