There's an argument to be made that WWE's babyfaces almost always have heelish aspects to their characters or their actions. D-Generation X, Ric Flair, and Eddie Guerrero would cheat to win whether playing the villain or the hero, and The Rock and John Cena have repeatedly been pilloried for allowing occasional misogynist and homophobic taunts to stay in their heavily scripted promos. In their most celebrated babyface runs, 'Stone Cold' Steve Austin had no friends and a history of assaulting anyone who came within stunning distance, while CM Punk was a pr*ck to pretty much everyone he met.
In comparison, the company's heels can often appear to be the more well-adjusted, rational characters on the roster. That's not necessarily a bad thing: after all, the best, most believable villains usually have complex motivations. A good maxim for portraying a heel in a pro wrestling angle is to find the rationale to the heels' villainous actions. Mick Foley recalls Michael Hayes telling him that, in his mind, the heel has to feel that his actions are justified. It doesn't matter how far out his motives - as long as he feels he's right.
The best heels are committed and headstrong in that belief: why else would they put themselves through so much grief? If their reason for doing what they were doing was just a bullsh*t smokescreen for them to be a douchecanoe, then they'd quit it and beg off the second that the babyface fronted up to them. No, all the good bad guys are right, in their own wrong way.
Not sure what I mean? Well, here's a list of ten examples that I just found conveniently lying about - most, of course, are dissections of heel turns, because these are usually the most dramatic instances of heelishness you could hope to find.