Waving at your neighbors is a show of friendliness.
Cornelius just checked his mailbox on the curb and sees his neighbor outside watering plants.
Cornelius wants to go back inside and watch TV.
Cornelius walks back to his house while waving to his neighbor, and asks him how his day is going.
Cornelius walks back to his house with his head down, ignoring his neighbor.
Cornelius' neighbor feels liked by Cornelius and feels good about himself and his neighborhood.
Cornelius' neighbor thinks that Cornelius doesn't like him and feels bad about himself and his neighborhood.