hold one's fire

abound in one's own sense

To follow one’s own inclinations and opinions.

ace up one's sleeve

A surprise advantage of which others are not aware.

act one's age

To behave in a manner appropriate to one's age.

act one's age, not one's shoe size

Synonym of act one's age (“to behave in a mature manner; to avoid being childish”).

add fuel to the fire

To worsen a conflict between people; to inflame an already tense situation.

afraid of one's own shadow

Exceptionally timid.

air one's dirty laundry in public

To reveal one's sordid secrets to the public.

air one's dirty linen in public

Synonym of air one's dirty laundry in public.