When I was younger I would go to the supermarket, get what I needed and pay without saying a word. I knew some kind of interaction was expected, but I couldn't

When I was younger I would go to the supermarket, get what I needed and pay without saying a word. I knew some kind of interaction was expected, but I couldn't make it up on the spot. By now, I have developed what can best be described as a large set of scripts in my head. I can go to the supermarket, the cheese shop, the butcher, etc. I can place my order, make smalltalk and appear as any normal person. The problems start when things go off-script, it's like mentally tripping over a loose tile. Worse even are situations that are new/unfamiliar. Explaining it has never really helped, people simply fail to understand. 99% of the time, I'm indistinguishable from a normal person. The problem with that is that people don't really see me as any different, and thus place the same expectations on me as they would on any other person. Even knowing that I'm autistic doesn't change this one bit. I've lost friends over misunderstandings where I failed to pick up 'obvious' subtext and they just refused to believe that I didn't see it. The worst part is where people get angry out of the blue and I have no idea why or what I did wrong.