The best testicles are the ones that hang low and dangle.
The testicles also produce a hormone called testosterone; this hormone in large doses is what makes a being grow into a male. Thus testicles are what makes a male a male!
Unfortunately for mammals, the testicles have to be on the outside of the body so that they do not get too warm. They are composed of tiny tubes or sperm ducts where the sperm are produced; these tubes are coiled up like very thin coils of spaghetti and are contained within an outer cover attached to the body by a thicker tube (the testicle or sperm chord). This chord has a thin walled swelling at the testicle end called the “Epididymis” and this is protected by being at the back of the testicle. This swelling is very important because it is where the sperm is stored and reaches full maturity after being produced in the sperm ducts or tubes. Both the testicles are contained in a special skin bag called the scrotum that adjusts to keep the testicles at the right temperature; closer to the body in cold external temperatures and further from the body in warm external temperatures.
Because they are delicate, testicles have many nerve endings and these are made to cause pain if struck or put under pressure so that the owner will take care not to damage them. This pain is extreme and is not solely confined to the testicles and even a fairly moderate blow can cause debilitation by causing the owner to go into shock; a very hard blow can not only rupture the testicle, but can cause so much shock that the owner dies.
Human nature being what it is, testicles are very often the subject of torture to force a man to tell all he knows as in almost all cases, no man can withstand the pain caused.
Women also find testicles a welcome vulnerability in an otherwise much stronger assailant in self-defence; the famous kick in the balls is a great equalizer.
Additionally, because testicles, along with the penis, are an observable difference in the sexes and because they are what make a man a man, they are often the target (both mental and real!) of female hate (and revenge!) for making men “the way they are”!