A few weeks ago, I copied the following from the Chicago Manual of Style Q and A:
Q. Oh, English-language gurus, is it ever proper to put a question mark and an exclamation mark at the end of a sentence in formal writing?
A. In formal writing, we allow both marks only in the event that the author was being physically assaulted while writing. Otherwise, no.
A discerning reader brought the interrobang to my attention. Now I thought the interrobang was some kind of science fiction apocalypse, but it turns out that I was wrong. The interrobang, according to Lord Internet, was created in the 1960s by an advertising executive. This raises red flags to the average copyeditor. If ad people ran the world, we’d have to put a “tm” after every word; “new discoveries” would be copyrighted by barnes and fucking noble; and all “c” words would be spelled with a “k” as in Krispy Kreme KakesTM Kourtesy of Barnes and Fucking Noble.
However the interrobang did gain a small cult following. There is a Word shortcut for it and a few typewriters did have an alternate interrobang key in the late sixties. Most interesting to me is the gnaborretni, which is the interrobang created with an upside-down question mark, used in Spanish.
Coolness factor aside, the interrobang is not standard and should not be used in formal writing. Sorry guys. But you can use the shit out of it in emails, science fiction stories about apocalypses, and as magazine titles and design firm names.