Because despite how obnoxious and out of control and rude and selfish my toddler often is, he's often more polite than most adults I encounter, including Yours Truly. At least my toddler has an excuse for those times that he behaves badly: He's a toddler. What's ours?
While it is never too early for adults to model positive behavior, there are a variety of areas in our lives that can include good manners. When and how to teach your child how to behave in these situations will vary depending on their age and development.