man up

verb /mænʌp/

a) to "be a man about it"; to do the things a good man is traditionally expected to do, such as: taking responsibility for the consequences of ones actions; displaying bravery or toughness in the face of adversity; providing for ones family, etc.

I was wondering when he would man up and marry that girl he knocked up.

b) (of military personnel in a unit) to assemble, each person manning (attending to) his station, prepared for departure of an aircraft, ship, etc.

You need to man up and confront your boss about his behavior.