Talking on the phone while serving customers is incredibly rude. Whatever you have to say, it can wait for your break.
Although I'll have to say the worst abuser of this that I've seen is a bus driver who was talking on the phone while driving. Not only rude, but also dangerous.
I play women's rugby for my college at Cambridge and, because our match was a 25 minute cycle away, we decided to book an 8 man taxi there, and one back. The taxi ride there was fine. However, the one on the way back was awful.
Firstly, they forgot to send an 8 man taxi, so half went back to college, and the other four of us stood (in torrential rain - it was awful!) for 15 minutes until another one came to pick us up. Now, as you can imagine, we were pretty muddy and wet, however, the taxi driver told us to hop in, and he took us back.
All was fine, until I got up, revealing dried mud on the seat. I felt bad because I hadn't realised my arse was muddy (or obviously I would have sat on a plastic bag or something) but offered to run and get a cloth/brush and clean it off, apologising profusely all the while. It wasn't that bad at all, because it had dried, and was only on one side of the seat, so I figured it would come off quickly. He refused my offer, and instead demanded we pay an eighty pound fine, then and there.
Obviously we thought that was ridiculous and asked to speak to his boss. The phone was engaged so the debate carried on an on. Would he let us clean it? No! It had to be done professionally, and it would take time out of his working schedule so we had to pay him the £80 fine right now!
By this point we'd been arguing for 10 minutes and he was blocking the front gate, so he moved his car and came inside our porters' lodge to argue some more. Luckily, one of the nice porters was on duty, who pointed out that it was a £40 fine for vomit in a taxi, so an £80 fine for dried mud was outrageous. The taxi driver told us we were all disrespectful, should never have got into his taxi in muddy clothes, were awful people and owed him his money then and there! When the porter asked us to take down his registration number so we could write a letter of complaint to the council, his tune changed. He said, grudgingly, that we could try and clean it. So we did.
It took one girl one minute to completely get rid of the dried on mud - it looked as good as new!
We apologised again for the mud, and said next time we would bring bags to sit on, to which he retorted that we should actually have showered and changed before we got in the taxi and were still bad people.
It would have been so much easier if he'd let us clean it off in the first place, rather than wasting 20 minutes of his (and our) time having a stupid argument, so he could sneakily get £80.