The antonyms for the word "most standup" could be "least upright", "most sit-down", or "most laid-back". These oppositional terms suggest a lack of firmness or stability, indicating a tendency towards relaxation or inactivity. While "most standup" implies confidence, strength, and conviction, these antonyms suggest the opposite: apprehension, weakness, or indecision. Therefore, depending on the context in which the term is used, these antonyms could provide additional nuance and meaning to the speaker's intended message. For example, if someone were to describe a business leader as "most standup", the antonyms might suggest that the leader is not as forceful or assertive as they appear.