The opposite of a crowning touch could be a blot, blemish or flaw. A crowning touch is an addition that enhances the beauty and value of something, while its antonyms take away from it. A blight or a setback could also be considered antonyms of a crowning touch because they represent a disappointment or failure. Whereas, substandard, poor and inadequate are other antonyms that represent a lack of excellence that a crowning touch symbolizes. A crowning touch is an embellishment that takes something to its highest level, its antonyms, however, diminishes its value and worth.