Look me in the eye and say goodbye

For the past few years I've noticed more often that people I've known, some for decades, do not look me in the eye. I can ask them a question and they can answer, but there will be zero eye contact. Zipping around the internet gives these possible explanations:

• Social Anxiety
• They Like You
• They Aren’t Interested in What You are Saying
• You Aren’t Visually Appealing
• Low Self Esteem
• They Are Hiding Something
• They Are Having a Bad Day
• They Don’t Want You to Think They Like You or Come Across as Flirty
•  They feel that you know a part of him that them they are ashamed of.
• They feel guilty of something
• You did something that they don't approve of and are trying to avoid you and the no eye contact is a hint for you to stay away.