Difficult question really. For me, the word "bitch" describes a particular type of behaviour which, although stereotypically considered to be inherently female, can also be applied to men. Being "bitchy", or "bitching" about something summarises the type of behaviour I mean, i.e. spiteful comments on someone's appearance, attitude or personality, whining on in a personal and spiteful way about someone or something. But I think this is very much a British interpretation of the word, and it may have completely different connotations in other countries.
As such, I tend not to be offended by its use, unless I am the one being called a bitch. But then, knowing I can be guilty of all those things at times, I would look at whether the slur against me was justified before complaining about it.
