I also prefer to be on the outside and don't like being part of a social group too long. I'm not sure why except that I'm used to being a loner and I feel judged by people becaise my family hated me and always told me everyone hates me. Did you have a past that conditioned you to think people will judge you?

You probably don't need to worry about boring a cashier so long as your conversation is not slowing the checkout process or preventing them from serving others. In a job like that, it's nice to have friendly customers because you occasionally get a really angry or difficult customer and a nice customers feels like a relief. Once I just said I had to hurry home because my dog had diarrhea and probably made a huge mess while I was shopping, and the cashier seem to find that pretty amusing.

In my 20s, I was always really nervous about encountering people to pay a bill or buy groceries. I used to be afraid people would get mad if I fumbled with my credit card or took too long to sign my name. I eventually realized that I was always afraid everyone would yell at me because my sister and stepfather constantly yelled at me for years. I was able to see objectively that cashiers are not likely to yell at me because most other people aren't bad people like my family were. After that, I gradually lost my fear of approaching people to pay for groceries and stuff. Maybe if you think about why you have your specific anxiety, you can diminish the power it has over you.