Nothing compared to some occupations such as a paramedic who come to the aid of injured pIssheads on a Friday night and get nothing but abuse.
If I was in the position of the checkout operator I'd be more focused on scanning their items as quick as I could than worrying about the customer on his phone.
At the end of the day, you come across rudeness everywhere you go, in work and out of work. I don't like it when I open or leave a door open for someone and they don't say thank you but I let it go over my head because it's not worth getting wound up about.
And for what it's worth I'm not one of these people who are forever gassing on their phone, so I'm not siding with the customer on that score. I just don't like jumped up oiks who think they can dictate to people when they have no right to - and especially to the paying customer.