Backslapper, by definition, is a person who is overly friendly or flattering, especially for personal gain. Antonyms for this term would include words that describe individuals lacking in these qualities. Words like unfriendly or unapproachable would denote someone who doesn't seek out friendships or engage in flattery. Aloof or detached would suggest an individual who keeps to themselves or doesn't appear interested in making connections. Another antonym could be modest or humble, as individuals who are not backslappers typically don't seek attention or make grandiose claims about themselves. In summary, antonyms for backslapper describe individuals who are reserved, honest, and humble.