He [truck driver] held the screen door a little open. "Week–ten days," he said. "Got to make a run to Tulsa, an' I never get back soon as I think." She [waitress] said crossly, "Don't let the flies in. Either go out or come in." "So long," he said, and pushed his way out. The screen door banged behind him. He stood in the sun, peeling the wrapper from a piece of gum. He was a heavy man, broad in the shoulders, thick in the stomach. His face was red and his blue eyes long and slitted from having squinted always at sharp light. He wore army trousers and high laced boots. Holding the stick of gum in front of his lips he called through the screen, "Well, don't do nothing you don't want me to hear about." The waitress was turned toward a mirror on the back wall. She grunted a reply. The truck driver gnawed down the stick of gum slowly, opening his jaws and lips wide with each bite. He shaped the gum in his mouth, rolled it under his tongue while he walked to the big red truck.
(John Steinbeck, The Grapes of Wrath)
I can’t understand what the highlighted part means. Is ‘nothing’ an emphatic word instead of ‘anything,’ and is the sentence after nothing, the complementing clause (or modifier) for nothing?