Lots of clients and even some of my friends don't like to use what I sometimes refer to as the 'P' word, they find it offensive, or 'don't like to think of you in that way'. I suspect their feelings on this come from a a mixture of things including the fact it's a taboo subject in society. To engage a 'prostitute' is considered wrong.
I've experienced the same. I have no problem with calling myself a prostitute, to me it's not a derogatory term in the slightest, but I have seen people (friends, family and clients) get offended when I refer to myself as such. They'd rather I stick with 'escort'.
I can't say I really understand why anybody would bother too much with the title - courtesan, escort, prostitute, call girl, working girl etc - they all entail the same thing - sucking cock for cash. I know it's about marketing to a certain extent but I also think a part of it is to do with people trying to establish hierarchies - courtesans think they're better than escorts, escorts think their better off than parlour girls and parlour girls look down their noses at street girls. But we all essentially do the same thing.
I find it a bit amusing to be honest and I think if you have to play silly games like that then you're probably not as happy with your chosen occupation as you would like others to think.