Scottish insult: "Your father is a representative of the Avon company"

The peak, the maximum, the be-all and end-all of humiliation. The ultimate insult of one's self, one's family and one's dignity. Consider all hope lost in your life if this is said to you. Use sparingly against enemies.

A stupid person; it refers to the lack of surface area on an individual's brain. The general thought is that the more surface area (wrinkles, creases, etc.) a brain has, the smarter the person is. Conversely, a person with a smooth brain (no wrinkles) has less surface area and would therefore be stupid.