Given that you don't believe there was anything wrong with the behavior, why is exposing it wrong?
Until the joke became public, the people mentioned in the joke (BO and his mom) suffered no insult, hurt feelings, or offense.
Upon the joke becoming public, however, these people are now faced with the prospect of being offended, having their feelings hurt, and feeling insulted.
So long as it remained private, the joke could not offend. The ones responsible for making the joke offensive were the ones responsible for making it public.
Jon
Love your enemies!