A taunt yelled at someone to let them know they are being a pussy and for them to get on with whatever they are afraid to do. Meaning to use the manly powers of a ballsack for courage.
When a woman is acting sheepish or timid about doing something, someone can inform that person, "To be a woman and grow a pair of tits".
This expression is derived from the term male colleagues would utter towards each other, if a member of the group is acting in a timid or sheepish manor regarding a certain situation, "Be a man and grow a pair of balls".