What does to write something behind the ears mean?

The phrase "to write something behind the ears" is not a common idiom or saying in English. It doesn't have a widely understood meaning.

It's possible that you're misremembering or misinterpreting something.

Could you please provide more context? Perhaps you heard this phrase in a specific situation, or it's related to a particular activity.

Knowing more about where you encountered this phrase would help me understand what you're asking and provide a more accurate response.