My friend thinks that I made a mistake but putting 'Duh?!'.
He says I should have put 'Duh!?'.
Is he right?
Multiple puntctuation marks at the end of the sentence are considered non-standard in formal writing but they are sometimes used informally, particularly "?!". From Wikipedia: "A sentence ending with an interrobang asks a question in an excited manner, expresses excitement or disbelief in the form of a question, or asks a rhetorical question. ...The question mark frequently comes first (to emphasize that it is a question), although there is no universal style rule on the subject."
Read more on the interrobang (or quesclamation mark) at:
Interrobang - Wikipedia, the free encyclopedia