When Lee barges into the production meeting carrying a stolen television set, Austin does not want to introduce him as his brother, as he does not want Kimmer to think he shares any similarities with this nomadic thief. Lee, however, makes sure that Saul knows exactly who he is. He is not the houseboy. He is not an appliance repairman. He is Austin's brother. Austin has spent most of his life trying to deny his family heritage—both to himself and to everyone else he meets. Lee is a nagging reminder of where Austin came from, and his physical presence is a fact that not even Austin can deny.
Indeed, all of Austin's efforts to escape his family are unequivocally denied. No one can escape his or her family. For Austin, this scene marks the beginning of the chickens coming home to roost. Lee knows he is supposed to stay away from the house until after six o'clock that evening, but comes home anyway. He claims to have lost track of the time, and maybe this is true. Nonetheless, we assume that Lee also wants to intentionally interrupt his brother's meeting with Saul, and that he knows how much his presence will embarrass Austin.
Scene three is where the real war begins. In the first two scenes there is hint and innuendo, but in this scene Lee actively begins to take over Austin's life. Whereas earlier Lee has represented simply a nuisance, he now begins to subvert and control Austin's screenwriting efforts. He sweet-talks Saul into a game of golf, and in the process effectively emasculates Austin by suggesting that Austin be their caddy. Saul, for his part, is taken with the mysterious stranger Lee. A character like Lee does not exist in his lexicon of Hollywood pleasantries and formalities. Lee is a wonderful salesman, and has none of the shame Austin has. By the end of the scene, Lee has secured the golf game with Saul, along with Saul's interest in an outline Lee plans to write.
Lee knows exactly how to sabotage his brother. Austin's professional success is the greatest sign of his independence from his family; by taking that success away, Lee begins to make Austin lose faith in the idea that he is "above" his family. The scene ends in silence, as Austin is flabbergasted by Lee's actions. Austin demands the return of his car keys, which were part of the original deal specifying that Lee stay away from the house while the producer was there. Unfortunately for Austin, Lee has no intentions of admitting any sort of breach of contract. The war is on. He refuses to return the keys, and instead gives Austin a big grin. Inside the grin is the invitation to war.