A person who votes against or excludes someone from a group, using the blackball system.
From 'blackball' (to reject via black ball voting) plus '-er' (one who does the action). Refers to the person casting the black ball.
The word 'blackballer' shows the power dynamics of exclusion—being the one to cast the black ball was so notable that it became a role, making social rejection formal and traceable.
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