The only character in Austen who displays what I consider ASD traits is Anne Steele from Sense & Sensibility. While many characters can't read a room, Anne tries several times to do things that are grossly rude, she has strange obsessions (the costs of Marianne's clothes and washing) and she never understands when people are lying. I'm no psychologist, but I do have a master's in cognitive neuroscience, so this isn't a complete layman's perspective.

Mr. Collins is just full of himself. He was also super lucky to get a living from Lady Catherine (livings could be sold for three times their yearly income) and is probably trying to flatter his way into another living (he could hold more than one).

Also, he is right, realistically, that Elizabeth cannot expect a better offer than his.