And how long before it's decided that I'm being rude for not making eye contact or replying to a question wrong, and then my appearence/behaviour starts being scrutinised whenever they see me?

All my little otherwise mostly unoffensive differences then start piling up and adding to any negative feelings these people have about me, and then one day it's decided that I'm just 'too spacy' so I must be 'on drugs' or my flinching at loud noises means I'm 'proper crazy'.

Then if I keep going to this shop and I ignore the random smirking/whispering from behind the counter and/or the security guard following half a step behind me, and I write off any hostile or weird behaviour towards me as these people obviously just having a bad day as surely it can't be my fault, I don't even recognise them etc, ... you can guess how charming people start being then, I'm sure.