Antonyms for the word "congenialness" typically describe a lack of friendliness or compatibility. Some antonyms might include "unpleasantness," "dislike," "incompatibility," "unfriendliness," and "antipathy." These words often connote an absence of warmth, kindness, or cordiality, and suggest a certain degree of discord or hostility. While "congenialness" suggests a sense of ease and compatibility, its antonyms point to the challenges that can arise when personalities clash or people disagree. In some cases, however, these antonyms might also suggest an absence of warmth or congeniality in a particular situation or environment, rather than in individual personalities or relationships.