passer un savon

To give someone a stern telling-off

It's what happens when someone gets a proper dressing-down for what they've done.

Le prof lui a passé un savon pour être arrivé en retard trois fois cette semaine.

The teacher gave him a telling-off for being late three times this week.

It traces back to women scrubbing laundry with soap and a wooden beating paddle at the communal wash-house. By the 17th century 'laver la tête' (to wash someone's head) meant to give someone a beating, which softened over time into a verbal one, and by the early 18th century 'savon' alone had come to mean a severe telling-off.