The fact is, almost all jokes are 'about' or 'at the expense of' some identifiable person or group. It may generalize about women or the clergy or politicians, ....or musicians..or it may go to old women, or southern politicians, or banjo players. And it may be so specific as to refer to individual old women, southern politicians, or banjo players....but at some point, you WILL find a level at which it offends someone..NO MATTER WHAT YOUR INTENTION!You just can't be sure unless you know your audience very well. Some women can laugh at 'some' PMS jokes, some clergy can laugh at 'some' clergy jokes, and some members of some ethnic groups can laugh at 'some' jokes about their own group...but it is all VERY content, locale, and situation dependent.
Why are stingy Scotsman jokes 'safer' than stingy Jewish merchant jokes? What makes jokes about Alzheimers (you meet new friends every day")cute at one moment and not the next? What makes 'Bobbit' jokes popular, even though they are always about a scary situation? What is 'funny' about misunderstandings due to deafness?
There are long answers to all of those questions, (many theses already written), but we KNOW that it can help to laugh so we don't cry. It takes work to make humor "work", instead of offend, and you could probably choose your closest friends on the basis of what you all laugh at. The only thing that is sure is that we will never all agree, and the "PC" arguments will go on forever.....