?!

From the Chicago Manual of Style:

Punctuation

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? This author is giving me a fit with some of her overkill emphases, and now there is this sentence that has both marks at the end. My everlasting gratitude for letting me know what I should tell this person.

A. In formal writing, we allow both marks only in the event that the author was being physically assaulted while writing. Otherwise, no.