(JTA) — Comedian Louis C.K.’s comeback attempt after a year of ugly sexual allegations hit another road bump this week, when audio emerged of a recent routine in which he has fun at the expense of the student survivors of the mass shooting in Parkland, Fla. — particularly the ones who became activists for gun safety.

“You’re not interesting cause you went to a high school where kids got shot,” says the comedian, suggesting kids should be out having a good time and not being politically correct. “Why does that mean I have to listen to you? How does that make you interesting? You didn’t get shot.”

C.K. often treads into taboo areas, but this is hardly his best work. And to understand why, it’s worth reading a tweet storm by Judd Apatow, the director and writer and force behind some of the top-grossing movie comedies of the past two decades. Apatow doesn’t lecture C.K. for being offensive; he carefully explains why the routine isn’t funny.

He puts his criticism into the context of the allegations against C.K., whose white-hot career on television and film was derailed after multiple accusations — which he has acknowledged — that he would corner women in order to masturbate in front of them.

It’s not just that C.K. is punching down — mocking someone more vulnerable than he. It’s that he makes himself the victim of others’ pain:

Apatow also defends his own right to be critical of another comic. It’s not censorship or political correctness, says Apatow, to say whether or not you like a comedy routine.

Ultimately, writes Apatow, C.K.’s routine fails because it doesn’t ring true. For a comedian like C.K., who has so often put truth-telling at the center of his act, that may be his most egregious comic sin: