give one's left nut

(slang) To pay for the privilege to do business with people at special events.

(slang, vulgar) To ejaculate.

(slang) To show off, or to excel.

A crude, vulgar slang phrase meaning to ejaculate. It sits firmly in the territory of explicit sexual slang, the kind of raw, unfiltered language that turns up in locker rooms, explicit rap lyrics, and adult comedy. Blunt, anatomical, and with zero ambiguity about what it means. Like many sexually explicit slang phrases, it's used both literally and sometimes hyperbolically to express intense excitement or shock — though the primary meaning is always the sexual one.