Wet behind the ears, also known as Green behind the ears, is a popular colloquialism, used to signify that the subject of the conversation is still a beginner in a certain field.
“Wet behind the ears” was adopted into the English language during the mid-1800’s, as a direct translation, or a calque from the German expression with the same meaning.
It first started appearing in colloquial contexts in the state of Pennsylvania during the 1850’s and started spreading and sprawling up variations in the Midwest during the following decades.
“Wet behind the ears” started gaining a wider popularity in the beginning of the 20th century, as it began to be featured in publications, novels, as well as theater plays and later movies, often associated with the Wild West.
Its popularity didn’t stop growing until the 2000’s, and it is still relatively prevalent in contemporary contexts.
“Wet behind the ears” was first defined on Urban Dictionary on February 14th, 2006.