I been living in Delhi for 7 yrs and I know quite a bit. If at all you need to talk to dhotis for any help or anything, refrain from speaking in Hindi, unless u r perfect in the language. Talk to them in English without fawning, try being a little hard but polite in tone, less chances they'll screw around. They get intimidated by anyone whos even remotely gora, speaking in english a case in point here.