A British slang word for a man's testicle — one of the two round sex parts that hang under the penis. People almost always say it in the plural, goolies, for the pair. It is not a doctor's word. Boys and men use it as a joke, or when someone gets hit there (a football in the goolies). It sounds a bit rude, but more like school humour than a heavy swear word. Older British speakers know it well; American English uses balls or nuts for the same joke. You would not put it in a formal letter or a textbook sentence, except to talk about the slang itself.

蛋蛋（英式俚語、開玩笑或帶點粗的說法）