a slap on the wrist
From Longman Dictionary of Contemporary Englisha slap on the wrista slap on the wristPUNISHa punishment that you think is not severe enough → slapExamples from the Corpusa slap on the wrist• So instead of a slap on the wrist I got promoted to high-flying executive symptoms.• In the past, officers who mistreated prisoners often received a mere slap on the wrist.• The fine was so low, it was little more than a slap on the wrist.