As far as derisive labels go, I've been thinking that enema bag has a much nastier tone and connotation than douche bag. And I like that it's unisex in nature. But it just doesn't roll off the tongue as nicely. That neat, crisp, percussive d at the beginning is so much stronger right out of the gate. Consonants are much more aggressive than vowels. As the Pythons would say, it's a good woody sounding word. And when you're putting someone down, I think we can all agree that woody is preferable to tinny.