nothing if not (something)
Most characteristically (something); (something) more than any other thing. In this phrase, "not" is always followed by a modifier of some kind that is emphasized as the most prominent attribute. He's nothing if not generous—that's his third donation this week. I am nothing if not patient, but even I have my breaking point.
nothing if not
Above all else, as in He was nothing if not discreet. Shakespeare used this idiom in Othello (2:1): "I am nothing if not critical." [c. 1600]