One of my favorite childhood memories consists of grabbing my younger sister by the forearm, holding her hand up at a ninety-degree angle, and slapping said hand across her own face, back and forth, back and forth. This sisterly gesture was always accompanied by my familiar chant of “Why ya hittin’ yourself, why ya hittin’ yourself?” over-and-over-and-over, in a kinda-but-not-really funny way. (Funny to the slapper. The slappee, not so much.)
In my defense, my little sis used this tactic on me as well, and she laughed herself silly when it was my turn to be the slappee. We just loved beating each other up. And I’m not using this expression vaguely, as in “beating up each other’s spirits” or “beating up each other’s self-esteem.” No. What I mean is: we really loved beating each other up.