When I worked in supermarkets I generally didn't care what a person was doing, as long as they didn't dawdle. Yes, it's nice if they ask you how you are or something, but if they were on a phone or something, that was their business, not mine, I just got on with my job.
Found it much more annoying working in a bar when people would come and order a drink, then go and ask what someone else who's part of their round wanted, order that, then them asking the next person, and so on. Stuff like that where you're holding me, and usually other customers up, THAT is annoying, and rude. However I still wouldn't tell them it was annoying me, all about customer service at the end of the day.