Wikipedia defines "bitch" as follows:
The term "bitch" comes from the 1150 word bicche, which was developed from the Old English word bicce. It also may have been derived from the Old Norse word bikkja for "female dog." The Oxford English Dictionary dates the term meaning "female dog" to around 1000 A.D.
As a derogatory term for women, it has been in use since the fourteenth or fifteenth century. Its earliest slang meaning mainly referred to sexual behavior, according to the English language historian Geoffrey Hughes: The early applications were to a promiscuous or sensual woman, a metaphorical extension of the behavior of a bitch in heat. Herein lies the original point of the powerful insult son of a bitch, found as biche sone ca. 1330 in Arthur and Merlin ... while in a spirited exchange in the Chester Play (ca. 1400) a character demands: “Whom callest thou queine, skabde bitch?” (“Who are you calling a whore, you miserable bitch?”).
Modern usage of the term describes someone who is "belligerent, unreasonable, rudely intrusive or aggressive." Of course, a man can easily be belligerent, unreasonable, rudely intrusive or aggressive, but when the term is applied to a man, it "is a derogatory term for a subordinate."
So, let's break this down. A female bitch is someone who acts in a traditionally masculine manner, and a male bitch is someone who acts in a traditionally feminine manner. While the history of the usage of the word clearly shows its female-specific and misogynist roots, it was later expanded as a way to apply to everyone who acted in a manner at odds with traditional gender roles.
Although I don't use the word often (I usually only use it to jokingly decribe myself during PMS or in some other humorously self-deprecating way), I prefer the de-connotative usage, summarized (by me) to describe someone who is unnecessarily rude, hostile, or critical. But when I use it, I am much less likely to call a man a bitch for the same reason. I'm also not at all likely to call a man a "bitch" and mean it in the modern context of "subordinate." In fact, I'm just wholly unlikely to ever call a man a bitch, for any reason. Why is that? I think it is because I don't want anyone I'm talking to to misunderstand and think that I am calling a man a bitch to illustrate how I think he is acting in a traditionally feminine manner, because using a pejorative against someone for not adhering to traditional gender roles is pretty much against everything I stand for. For some reason, though, I assume people will understand that if I refer to a woman as a bitch, that I'm not calling her a canine in heat.
Another interesting phenomenon that I see happening (and that I use often, myself) is eliminating the female-specific insults from our collective vocabulary and replacing them with traditionally male insults, like "asshole," or even the milder "jerk." Since, in addition to not using gender-based insults, I also actively avoid genital-related insults like "pussy" or "dick," I have been embracing "asshole" and "jerk" as general insults, as neither implies a gender and, although traditionally reserved for men, are perfectly descriptive of what I am trying to call out in the other person.
Something, though, makes me feel uncomfortable about taking a term reserved primarily for men and using it for women and men alike, and I'm not sure why. When describing a role that remains identical whether a male or female performs it that English has unnecessarily divided into genders, like actor and actress, for example, I try to default to the "male" word. So, I'm more likely to call Jennifer Connelly an actor rather than an actress, because I see no reason to differentiate. Who cares if Jennifer Connelly is male or female, when "actor" and "actress" mean exactly the same thing?
So, why eliminate "bitch" from my vocabulary? I'm not sure that I will. But in order to be consistent, it seems that I should. But... why not just call everyone who is acting like an asshole a "bitch," instead? Whether they're male or female? Maybe it seems easier to say "asshole" or other usually male-specific terms, because we all know that they mean the same thing whether applied to men or women, and even though "bitch" arguably means exactly the same thing as "asshole," people are likely to be widely misunderstood about the intent of the insult when used against a man.
Again, though, there's a certain level of discomfort in reverting to historically male-centric language that does not reconcile well with my preference for egalitarianism (with the exception of actor/actress, as can be seen in the Wikipedia link's "terminology" section). I don't like male-as-default language, at all, so treating words that originally conjured up an image of a man as if they are for all of us, while treating words that originally conjured up an image of a female as off-limits feels quite misogynist to me. Society already insults men by calling them women; it feels as though avoiding using traditionally feminine terms to describe men is perpetuating the widespread (if not subconscious) belief that the worst thing a man can do is be like a woman.
Do you use the word "bitch"? How do you feel about gender-specific insults or descriptors?