I know this is an old thread, but in case there are any new readers....way back in the old days when I went to nursing school
, we were told to bathe everything else first, then hand the soapy cloth to the person and tell them they could "finish the bath", then be there with a clean cloth or 2 to rinse. This gives them a little privacy and most people can reach that part of their body to "finish the bath". If not, then they probably are not in any condition to be embarassed or to embarrass you.
As far as crude remarks, I have only had a few (probably cause I work in ER and we don't generally do baths). Most have come from drunks and are not worthy of comment. If it continues, then I tell them they can lay there in their own vomit, urine, feces, etc. until they can show some decency. If not, then they lay in it. As a human being, I don't have to put up with their crap. It is my responsibilty to offer to help them get clean, but responsibility runs both ways.
Sometimes being old and crotchety has it's rewards.