My late Father never swore in front of family or friends - but he did used to swear when he thought that he wasn't being overheard. When I was a teenager I used to lie in bed on a Sunday morning while my Mother went to church and my Dad went to work in his shed. After a while he would start crashing about and swearing to himself: "where's that f**cking screwdriver/hammer/clamp etc.? I can never f**cking find anything in this f**cking place ... and on and on in much the same vein. I suppose he thought that no-one could hear him in the shed - although I suspect that half the street could hear him!