keller efers to himself as stupid many times. why do you think he says this?

Keller enters, and they lightheartedly banter about his lack of education. Keller says that everybody is getting so educated that there will be no one left to take away the garbage. "It's gettin' so the only dumb ones left are the bosses ... you stand on the street today and spit, you're gonna hit a college man." Joe is keenly aware that he is not an educated man. This becomes one of his excuses or justifications for his criminal actions.