Never get angry and sweary with call centre people
For my sins, I spent a uni summer break working in a call centre many moons ago, and the people who go apoplectic with rage are the ones who really brighten up an otherwise incredibly dull day.

The more inventive you are with the swearing, the funnier it becomes, and they're more likely to rebook you for a return call, with either a note, saying "This guy is REALLY nice, but couldn't spare the time when we called, please ring back on ..." (In order to wind up their colleagues), or they'll just note you as a mentalist who'll cheer you up with some colourful language.
( HoratioFellatio Taking the the out of psychotherapist, Fri 28 May 2010, 18:26, Reply)