I one took on an evening job with a telemarketing company in London, selling double glazing. Thirty telemarketers cramped in a small room with telephone directories and headsets. The supervisor was just like Nicky Katt in the 'Boiler Room', played brilliantly by Greg Weinstein (see image below).
He hurled abuse at us if we weren't trying hard enough to clinch deals. Things like "pitch 'till you're on your knees or I'll shove that headset up your ____", or (you’ll love this) "dump the bitch", if an old lady was answering too slowly.
If that wasn't enough, the abuse from targeted customers was sometimes vile (and many do blow loud whistles down the phone). After all we were often ringing during their evening meal, or as I remember on one notable occasion, as one family were waiting from an important call from the local hospital following a serious injury to a relative.
I turned up the third evening drunk after drinking Ouzo all afternoon in a Greek cafe. I have never been so charming. I didn't sell any double glazing, but I chatted to some lovely people about their holidays and helped a pensioner sort out her utility bills, until of course Mr Katt arranged for two heavies to eject me from the building.
It's a bad industry. I agree with Fryke, it's better to avoid rudeness, but if you lose your cool don't worry, the staff will probably just take it in their stride.