I think it's easier to be rude to faceless people. And also you do tend to be calling because of a problem - so likely to be annoyed.
But some staff are good, some are not. And in my experience, UK call centres are better than overseas. Simply more polite. I think it may be a not first language thing... Tone of voice is so important when you have no body language.
I spent an hour on the phone to Vodafone on Friday. Their admission, their system has cocked up. I want to port over an existing number. I have a temporary Vodafone number. Which they gave me. Which doesn't exist on their system. I shit you not. It's Kafka-esque. They cannot find me by phone number, account number, address... The phone works though!
So I did an full hour with one guy, on and off hold, all the while we were chatting and laughing. At one point he said he had to give up and could I go into store. I said, "look, I'm going to sound stroppy now and you must not take it personally - but no, I'm not doing a 2 hour round trip when it's your fault". And asked for his manager. And first thing I said to her was that her been great and please not to take my request for her as anything negative on how he'd handled the issue.
So - low stress levels, despite over an hour and no resolution.
An hour later, I've got what sounded like an offshore guy, by his English. Within 3 minutes, I heard my voice rise, and I hung up on him. I did actually say, "look, you're not listening to me and I am hanging up on you". But he was downright bloody rude.
Example: when you call Vodafone, you have to type in your number. It gives you 3 attempts then cuts off the call. When their system doesn't recognise their number, this means you can't get through. I managed it by entering a friend's number!
I tried to explain this and in a rude tone he cut right across me and said I should have pressed 0 (the message doesn't say this).
He should have said "I'm sorry, that would have been frustrating. You can actually cut out that part by dialling 0..."
Seriously. An hour with one guy and I'm still smiling, 3 minutes with the next and I hang up on him.