The opposite of the phrase 'most unprotesting' encompasses a range of different antonyms, depending on the context. Perhaps a more general antonym would be someone who is rather vocal and willing to speak up when something is bothering them, as opposed to being silent and uncomplaining. In this case, some antonyms might include 'outspoken', 'vocal', 'disobedient', 'argumentative', or simply 'protesting'. If we're specifically talking about someone who is effortlessly compliant and easy to deal with, antonyms could include more negative terms like 'difficult', 'uncooperative', or 'unyielding'. Regardless of the specific context, however, the common thread among all of these antonyms is a general lack of willingness to simply accept things as they are without question or resistance.