Willie is Maya's uncle. And we're not talking Baxter-style uncles, who are totally mean and can kick a guy to death. He is a disciplinarian, though. And he's not joking around. He makes sure Maya and Bailey Jr. know their multiplication tables by threatening to burn them against their kitchen stove. Gulp.
Uncle Willie's defining characteristic is his disability: he walks with a cane, his left hand is atrophied, and the left side of his face is paralyzed so that he has difficulty speaking. Because of this, Willie is the butt of all jokes in (mean-spirited) Stamps. But this guy is a proud man, and he doesn't let the bullying get to him. Instead, he wears fancy clothes and puts on a strong face.
Despite his pride and strength, Willie crumbles one time. When two teachers with a fancy car visit the Store, he pretends that he can walk and speak normally. Why do you think he pretends this one time? Why does it matter that strangers think differently of him? Does he want to fit in, just this once, or is there something deeper going on?