We taught our son to say bye-bye whenever somebody leaves and he did pretty well. He used to wave bye-bye everytime his dad leaves for work but just recently he just quit doing it. What he does when his father gets out the door he runs straight to the window facing the driveway and if the blind isn't open he would lift it up and look outside. He then smiles and waits until the car disappears from his sight. He does this with his brother's girlfriend too, all the time but never with his brother. He did it last night that dada laughed so hard at his boy's antics.