Tonight at dinner, my nerd friends and I got into a discussion about the mostly female but sometimes male compulsion to "fix" one's romantic partner, and spurred by this, I figured it was about time to write a meta that has long been brewing in my mind about the phenomenon of Bad Boys.
I recall a conversation on Fandom Wank where people were talking about how the fangirls love Zuko because he's a "bad boy," and one person was like "What? Since when is Zuko a 'bad boy'? He's a total dork!" They were right of course, and this led me to a realization: Regarding the old maxim "All Girls Want Bad Boys," the phrase "bad boy" refers to two different character archetypes.
Type A is the motorcycle-riding bad boy. His "bad"-ness comes from his being a rebel. He smokes, drinks, partakes of illegal substances, causes trouble, gets in fights, only goes to school when he feels like it, probably has lots of tattoos and piercings and maybe an outlandish hairdo. He's the type of guy you'd date because he freaks out your parents. Women are drawn to him because they know that life with him could never be boring. He's usually not evil by any stretch of the imagination; he's just... dangerous.
Type B is what I like to call the "fixer-upper." His "bad"-ness comes from his being a villain, or at least an anti-hero, and being evil to some extent, or at least a big jerk. However he has a few humanizing qualities, whether a hint of a heart of gold buried under all that puppy-kicking, or a tragic past that explains why he ended up a douchebag, or some secret angst that he hides behind a façade of indestructibility — whatever the details, it's clear that he has the potential to be redeemed. Women are drawn to him because he's damaged and they believe they can "fix" him, usually with the power of love and boinking.
The two types have a number of other distinguishing features that make them easier to tell apart. For example, if your bad boy is a seductive ladies' man, then you're definitely dealing with a Type A. Type Bs are usually way too wrapped up in their own evil plans and angsting to even notice girls, much less chat them up — look no further than Sasuke and Zuko for examples of this. The Type A, on the other hand, is much more likely to be aware of the effect he has on girls and to use it to his advantage, à la Rich from "Penny & Aggie." Actually, coolness in general is a trait more associated with Type As — James Bond is a great example of a post-high-school Type A. Type Bs are more likely to be complete dorks who take themselves extremely seriously — again, Zuko is a shining example of this. Relatedly, snarking and witty dialogue is another Type A trait — Spike from Buffy strikes me as being a Type A for this and other reasons, at least before his Spikeification.
Basically the difference between the two types boils down to the core appeal of each. Type A is appealing because he's fun and exciting and dangerous; Type B is appealing because he's a "project."
However obviously categories like this are never ironclad, and there are plenty of characters who are a mixture of Types A and B. For example, Ikuto from Shugo Chara is my pick for "Bad Boy Most Likely To Have Been Concocted By Evil Geniuses Who Are Now Fabulously Wealthy" because he's such a perfect combination of both types: he has all the style and flair and seductive "you know you want me" quality of a Type A, plus all the hidden angst and "I'm not evil, I just need a hug" appeal of a Type B.
Come to think of it, a hybrid of both types seems like the optimal form of bad boy, or at least it's what the fangirls seem to prefer. If you have a bad boy who does slot neatly into one of the types, you can bet there'll be a mountain of fanfic in which the fic-writers supplement his personality with traits from the opposite type. It seems like fangirls want their leather-wearing charmers to also have angst and need comforting, and they want their angsty projects to also be smooth snarky seducers who know how to romance a lady. Just look at Draco Malfoy: in the canon he's a staunch Type B, but fandom likes to add a bunch of Type A traits to him, including those memetic leather pants which are straight out of the motorcycle-riding Type A's wardrobe. Or as Fandom Wank Wiki puts it: "In fanon, Draco is known for his cool dialogue and a tendency to wear leather trousers. In canon, Draco is known for barely managing a decent put-down on Ron and a tendency to cry like a little girl in the bathroom." (Of course, crying like a little girl in the bathroom is exactly what makes fangirls flock to guys like Draco in the first place.) Zuko is another clear Type B who gets Type A traits awkwardly shoehorned onto him in fanon, resulting in unintentionally hilarious fics where Mr. "You're Beautiful When You Hate The World" is portrayed as a smooth ladykiller.
As for the reverse — a Type A being supplemented with Type B traits in fanon — that seems to happen less with conventional Type As and more with a subset of Type As who have all the style and lady-charming and witty dialogue and "cool" factor of the average Type A but buck the "not evil, just dangerous" stipulation by instead being 100% evil. I guess you could call this the Evil Is Sexy subset. Anyway, these guys have a lot of the same "fun and exciting" appeal as the standard Type A, but the fic writers often compulsively tack on a tragic backstory to make these dudes more palatable and to give them bonus Type B appeal. Because I guess we can't just enjoy a sexy villain for what he is; we have to humanize him too, which tends to defang him somewhat. (Sometimes this even happens in canon, which I gather is what happened to Spike.) Perhaps it's also to assuage the guilt of perving over an unrepentant douchebag.
Of course, sometimes these varieties of canon-warping can happen to characters who fit neither of these types and who honestly can't be categorized as "bad boys" at all. Just look at Itachi from Naruto. Before the circa-chapter-400 revelation that turned him into a Type B, Itachi was just a blank slate, a plot device with zero personality beyond "stoic" and "unfettered." He was just a random evil guy, lacking both the charm of the Type A and the redemptive potential of the Type B, and yet fangirls often ascribed one or both of those personalities to him in fanwork depending on their tastes. Or heck, look at Draco Malfoy. He became a Type B in the later books, but before that, he was neither type. He wasn't a cool villain — quite the opposite, he was a whiny sniveling little worm and a frequent butt of jokes — but he was also pretty two-dimensional in his villainy, with no hint of a nicer side. But even back then, the fangirls couldn't get enough of him and would subject him to either or both varieties of personality-warping. And wardrobe-warping, natch.
So I guess there are two larger categories of "bad boy": on the one hand, you have the Canon Bad Boys, whose canonical personality fits into Type A, Type B, or both; on the other hand, you have the Potential Bad Boys, who are just assholes in canon, but who, with a little tweaking of personality, could potentially be transformed into genuine "bad boys" of either or both types, with said transformation happening usually in fanon but also sometimes in canon.
Anyway, in conclusion, the term "bad boy" actually encompasses a wide range of personality traits, character types, and audience appeals, to the point where the only thing that unites all the "bad boy" characters under one umbrella is the reaction they provoke in a certain segment of the audience. By which I mean: they cause a lot of panties to become moist.