Obligatory, judicial, slap on the wrist
a slap on the wrist so light it might as well be a pat on the back from a giant chicken
He got a slap on the wrist for talking back to his boss and then went on a lunch break.
The teacher gave her a slap on the wrist for drawing on the desk and said, 'That’s the least I could do.'
He got slapped on the wrist for being late and then got a free coffee.