"Finally, I note that he describes the title of my book as “obscene,” and complains that it attacks someone who is “elderly.” Would he care to say where the obscenity lies?"

Hitchens doesn't deny that there is a sexual connotation. Regardless, sexual connotation is not synonymous with obscenity. The point is that he invites Leys to discuss whether the title is obscene or not. (He doesn't explicitly deny the claim of obscenity, you'll note.) This discussion would further Hitchens's goal of discussing religious wfigures with less reverence.

p.s. I'm not the one downvoting you, if it matters.

EDIT The meaning of the word "obscenity" is quite clear, just saying something is obscene does not make it so. If you are asserting there was obscene content you should support your assertion and say what the obscenity was.

If you didn't know that, I understand that you might not see the sexual connotations of such a title. But please don't tell me Hitchens didn't know, it would be the most formidable misunderstanding in the history of debating.