Anyway, in medieval times, Catholic bishops performing confirmations began giving each confirmand a slap on the cheek. It wasn't a very hard slap, to be sure; it was entirely symbolic. You see, in ancient Roman law, followed in Gaul and other places, a slave would be so slapped by his master upon being set free. So it was sort of a rite of adulthood, a recognition that you were responsible for yourself now, no longer depending upon the vows taken by your parents at your baptism.
Fast forward to Ireland early in the last century. A visiting bishop was in some village church to confirm some young people, among whom was a particularly rowdy boy from a family of "fighting Irish." When the frail old man lightly slapped the boy while he was kneeling, the surprised confirmand promptly stood up and cold-cocked the bishop.