The correct option is A clumsy
Debonair means (of a man) confident, stylish, and charming. The opposite of debonair is clumsy, or awkward in movement or in handling things. Hence, Option B is correct. Among the rest of the options, stiff means not easily bent or changed in shape, courteous means polite, respectful, or considerate in manner, pleasant means appealing to the senses. These do not express this antonym, hence incorrect.