The other day I was arguing with someone at work about going to a potluck lunch. I wanted to go. The other person -- from some personal motive I was unable to dig out -- didn't. Later, when I was wondering why I had to be so self-righteous about it, I thought, well, you're Pig Will and she's Pig Won't.
Pig Will, in case you don't remember your Richard Scarry, is kind, cheerful, polite, helpful to his mother and always keeps his room clean. Pig Won't is obstinate, sloppy and defiant. As a child it was clear to me that Richard Scarry had based Pig Won't on my younger brother. This left me with Pig Will, and I've been Pig Will pretty much ever since (except for the keeping your room clean part.)
I love the look on Pig Won't's face, by the way. He knows he's in trouble, but he's pretty sure his mother's going to get him out ot it.
Of course, as a writer, you want to make your characters more than simple good and bad. Even Pig Wills are conflicted and often they rebel. And Pig Won'ts -- well, like the mother in the picture, they often call upon the reader's sympathy.