Another problem is that claiming something is a joke would not let you off the SJW hook. Every single instance of blackface has been a joke. Every rape joke is, tautologically, a joke. There is no joke more archetypical than Count Dankula teaching his pug to sieg heil, but he still got fined. Indeed at least 80% of what SJWs want to cancel are jokes (the rest are factual statements like "transwomen are men" and "blacks are academically underachievers and are prone to criminality"). In a society so puritanical as to penalize speech, claiming your offending statements as "jokes" would only add to the crime.
And who are Bobby trying to impress anyway? SJWs will not accept his "joke" defense. Reasonable people like us will laugh and let him pass if we are convinced he has really been joking -- but the fact is that we aren't convinced at all! The frequency, the virulence, and the way his hateful rhetorics has rubbed off on his idiot little brother all tell us that he means every word of it. So the only possibility is that Bobby defends himself from himself. He keeps repeating this lie to himself, to convince himself that he is a good person, despite people shaking their fists at his genocidal rage.