Thinking back, I got extremely stressed out when shopping when I first moved here. I think for me, it was people getting up close, or just reaching over me to grab something off the shelf (without giving any warning beforehand - like an "excuse me" to make me aware of what they were going to do), or even jumping in front of me while I was standing there trying to get my things off the shelf, if you know what I mean.
This stressed me out, too.
But what drove me to tears was packing my own groceries. - Now, I've packed my own groceries in the US, so I don't have a problem with that. In fact, I prefer to pack things myself because I'm picky about where the items go in the bag.
However, in the US, the cashier would watch me and lend a hand if they could. They treated me like I was "the customer" until I picked up my packed bags and walked away from the counter.
In the UK, it used to take me forever just to get the carrier bags open (the sides stick together), and while I was still doing that, the cashier would be ringing up the next person's items and throwing them on top of mine. Then, the next person would be packing their groceries while I was still packing my groceries, in the tiny little space at the end of the counter, so that I was shoved into a teeny corner.
I now know to bring my own cloth bags so I don't have to deal wth opening the plastic carrier bags, and I don't take my wallet out of my handbag until I've packed everything just the way I like it. - The cashier and everyone behind me in the queue just have to wait.
But it was very upsetting, to the point where I just didn't want to go shopping.