>US showed an inverted bell curve, when frequency of the language was plotted against the socio-economic-educational background of the speaker. Briefly, the higher or lower the station of the speaker, the more vulgar the language.

I'd agree with this. I had a wide range of friends whilst at university and noticed that the "upper classes" swore like troopers and had no problem with "personal habits" that would be regarded with horror outside their social circle. That which was allowed "Upstairs" would not be countenanced "Downstairs".