To slap someone on the ear as a punishment.
Someone, often a parent, smacks a child on the side of the head, on the ear. The slapper might hit first one ear, then the other, or both at the same time. Or it might be one adult doing it to another.
American football rules, fortunately, prohibit a simultaneous slap to the earholes of the opponent’s helmet: once legal, it was banned because eardrums were injured by the sudden air pressure concussion.
The noun “box” (defined by the OED as “a slap or a cuff on the ear or side of the head” has been used in the singular (“a box on the ear”) since the 15th century
Any number of historical and literary characters have been recorded as “boxing someone’s ears.” For example, in 1598 the Earl of Essex offended Queen Elizabeth I; eyewitnesses reported that Good Queen Bess promptly “boxed his ears.” This certainly means that she smacked him over each ear.
My mother used to threaten me with the words, “I’ll give you a thick ear!” when I was a child and had done something she didn’t like. I’ve never heard that phrase anywhere else and assume it is a British expression, since Britain was where she grew up.
She usually carried through on her threat, and I remember how much it hurt, so I hope that kind of punishment is a thing of the past.
If so, then everyone will be able to “lend an ear” (a healthy ear) to listen in a patient and sympathetic way to someone’s story.