Once upon a time, there was a short person who lived in a very short house. He wanted to grow tall and live without ever being called Short.
His neighbours were of different shapes and colours. Each shape had different lines at various angles and edges. Each colour had different shades. Short thought he also needed a distinct feature and thus created a standard by his height.
So with the help of his neighbours he made a line at the bottom of his feet and the top of his head while lying flat on a large piece of wood. He continued to do so till the large piece of wood ran out.
He then counted the number of lines he had made. It totalled to 31 lines included the initial one. He numbered them from 0 to 30. He wondered what he should call his new creation. He thought about it and called it a ruler. Which roughly meant as a guide or measure. He then had to think of what each line or unit should be called.
He thought and thought and finally decided to called it after his own name Mr. Cm. The centimetre - The short distance between the ground underneath his feet to the point just above his head. And he named the 30 cm ruler after his best friend - the foot. And as he jokes about with foot being single, Mr. Cm teased him once saying when Foot does get married they would then be plural as in Feet.
Thus the standard of cm, foot and feet came about.