Q. I checked throughout CMOS and found not a single mention of the interrobang. How could there not even be a single mention of such an intriguing punctuation option?!
A. And we don’t mention smiley faces, either! But some of us are keeping a list for the next edition.
[Editor’s update: Smiley faces are now mentioned in the usage glossary in chapter 5, under “emoji; emoticon.” See also CMOS 10.78 (which features an actual smiley face). No interrobangs yet, but here’s one to tide you over: ‽ (that’s Unicode 203D for those keeping score).]