Telling is not the issue. Telling, not moving on quickly — and not expecting any repercussions for your racist ignorance/ innocence are the problems.
If he was so intelligent and self-aware he’d know that. For blacks it’s kind of like being our boss the suddenly one day you come in and call us a nigger. Then you come to work everyday after— in our faces — with a smile and kind voice.
It’s killing us softly. It’s an invisible cut everyday he stays. And it gives people the greenlight to keep doing it at the expense of innocent people. Especially if he’s allowed to rule over the people he’s insulted. Don’t do it would be my first piece of advice. But if you do and it’s found out, take the punishment and move on. In life, you must face consequences for any action you take.