I'm a IT tech and most of the time our customers are calm and understanding and leave me alone while I work. And then we have those who tell you what's wrong, why can't I fix it fast enough, and “no you're not hearing me! I'm telling you it's this!”
I worked in my family's small business and my parents would just smirk and say you can leave then.
I got in trouble because I told the customer he was interfering (being an asshole) and got written up for it. I hate this