This beauty was spoken by a confident attorney prior to a hearing. It is a congruent conflation of “on the fly” and “off the cuff”, both meaning to do something quickly and without thinking carefully before they do it. Mixing “on” and “off” is certainly a part of this malaphor, and perhaps “fly” and “cuff”, as both can be articles of clothing? Using “off” instead of “on” actually makes more sense as an airplane “flies off” to somewhere. “Fly off” means to go in a hurry, similar to the meaning of this malaphor. The speaker perhaps just inverted the words “fly” and “off”. A big thanks to Sam Edelmann for hearing his one and passing it along.