Past tense of chump: to act foolishly or be tricked, or to chew heavily.
From 'chump,' which may be a blend of 'chunk' and 'jump,' or possibly imitative like 'chump' for heavy chewing. The sense 'to trick' evolved from the noun 'chump' meaning a foolish person.
Getting 'chumped' means you fell for something stupid—the word perfectly captures that frustrated feeling when you realize you were duped by someone obvious.
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