The Shadow of a Bruise
Don wasn't a genius, but he was smart.
So when he hit Charlie, he landed a clean blow to the stomach where the bruise wouldn't be visible. Charlie got hit often enough that Don could have chanced a blow to the face and had the pleasure of viewing his handiwork every time Charlie walked into his classroom.
But, in the end, he had marked Charlie in a way that no one else ever could. Bruises purpled and faded, but Charlie's look of hurt and fear lasted a long time.
Author's note: I think it's perfectly conceivable that Don would have hit Charlie at some point when they were growing up, and not in a roughhouse, fun way. I'm planning to write at least three drabbles exploring a situation and motivation for their encounter. My focus is primarily on motivation.
On that note, I felt my own perception of Don's motivation shifted while I was working on this piece, so I'd be interested in your perspectives on his actions in this, both for ideas and to see how well I communicated my message.