heleninwales has been talking about learning Welsh and the resulting unintentional offence given when beginners mix up the intimate/formal terms of address. It reminded me of a story told to me by a bookshop owner in a little village in the Yorkshire Dales. Apparently there used to be this difference in Yorkshire dialect. The familiar form of address being 'thoo' and the formal one being 'thou'. (The use of thee, thou and thy survives to this day in the dialect of my part of the Yorkshire, much further south in the county, but I'd never heard of the 'thoo' form.)
So the example goes...
A farmer takes on a new apprentice and works with him closely for the first day. By supper time the boy is addressing the farmer as 'thoo.' Offended at the familiarity, the farmer turns to him sternly and says.
'Dun't thee thoo me 'til ah thoos thee first!'