Introducing yourself to someone you have never met is polite.
Jack is having lunch with his friend Justin at their house and Justin's mom walks by their table.
Jack wants to have an enjoyable lunch with Justin.
Jack introduces himself to Justin's mom, and they continue their lunch.
Jack ignores Justin's mom and continues to talk to Justin avoiding an introduction.
Justin's mom states that Jack seems like a nice friend and leaves them to their lunch.
Justin's mom states that Jack has made a bad impression and does not want him inside the house anymore.