To firmly grasp and stroke the, baseball bat sized, hot, sweaty and slippery meat shaft attached to the underside of a stallion, which commonly known as a horses cock. This act is generally frowned upon in most societies. It it is simply unforgivable to any and all people who attempt it and succeed. It is even especially unforgivable (and uncontrollably hilarious) to proceed to drink any/all of the horse cum that may ejaculate violently into the milker's face.
Used as an exclamation when noting an obvious or moronic error in judgment. Usually suggesting complete unworkability. Also used to designate a situationone tries to take advantage of, where there is no actual advantage to be had.
#1: "I really thought my new pet snake and my hamster would get along. Well, I guess you can't milk a horse."
#2: Jerry - "So I tried to milk this horse and well... you know what they say: 'You can't milk a horse'."
#3: Fred - "I just tried to hit on Nancy at her ex's funeral, but ya can't milk a horse."
#4: "I invested $8,000,000 on the new line of Pogs, but goddam: Ya can't milk a horse!"
n. software that is no longer sold or supported by the original publisher / developer, often found as free downloads on the internet because it cannot be obtained elsewhere. Not legal, but often seen as morally acceptable because the company that made it is no longer selling the title, nor releasing it as freeware, therefore abandonware is "keeping the gamealive", so to speak.
Doom II is not abandonware because idstill sells it, while The Incredible Machine is not sold, therefore is abandonware.