This is an expression used to denote something that is irrelevant, useless or unfit for purpose. If you wanted to say someone was stupid, you could say “Her head is as empty as a eunuch’s ball sack.” If you wanted to say someone was useless, “He’s as much use as a eunuch’s ball sack.” Cowardly “If courage was balls you’d be a eunuch’s ball sack.” The expression is versatile and can be adapted to a wide variety of purposes.
by AKACroatalin April 21, 2015