There isn't a single word antonym for "man up," but here are some options depending on the context:
General antonyms:
* Give up: This implies surrendering to a challenge or difficulty.
* Back down: This means to retreat or yield in the face of opposition.
* Avoid responsibility: This means to shy away from taking ownership of one's actions.
* Be weak: This refers to lacking strength or courage.
* Be afraid: This implies feeling fear or apprehension.
Antonyms that emphasize a lack of courage or decisiveness:
* Chicken out: This implies being cowardly or afraid to act.
* Be a wimp: This is a derogatory term for someone who is weak or cowardly.
* Be a scaredy-cat: This is a childish term for someone who is easily frightened.
* Be timid: This means to be shy or hesitant.
* Be a pushover: This means to be easily manipulated or persuaded.
Antonyms that emphasize inaction:
* Do nothing: This implies refusing to take any action at all.
* Sit back and watch: This means to passively observe without participating.
* Ignore the problem: This means to pretend that a problem doesn't exist.
* Procrastinate: This means to delay taking action.
The best antonym for "man up" will depend on the specific context and the intended meaning.