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.
"Everyone check it out! Nadsack is about to milk a horse!!!"
by cockjuggling thundercunt June 23, 2009
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stallion: masturbating (jacking off) a horse until the stallion goes into climax and ejaculates
mare: grabbing the mare's udder, squeezing it until the udder shoots out the milk
in jackass number two, they were milking a horse (stallion) in a stunt called "how to milk a horse"
by curtis450 December 22, 2017
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Used as an exclamation when noting an obvious or moronic error in judgment. Usually suggesting complete unworkability. Also used to designate a situation one 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!"
by Skazu March 4, 2010
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When you accidentally show up to the wrong place.
"Hey man you almost here?"

"Nah man I milk horsed it I'll be there in 5"
by Chadsdong November 5, 2017
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