I have only once sworn at a stranger. It was a car dealer I told him that I would ring him up and please do not contact me before 4pm as I was night shift. So at 2.45pm he rang me and wanted to chat about cars I told him to go away I was asleap (using the f bom) and put the phone down. Normally I wouldn't do that but I told him I would be asleap I also warned him that I don't take being woken up well either.