Donkey dust is slang for ketamine, a widely used medical dissociative anesthetic with a major recreational black market. Ketamine users are also known as "zombies" or "ketapillars" because after hoovering too many rails, they lose the ability to walk on two feet, resorting to quadrupedal perambulation.
In the mythical stages of ketamine intoxication, the donkey phase precedes the ketapillar, and the ketapillar phase precedes the legendary k hole.
ORIGIN from modern English donkey (slang for "doofus") + dust.
Etymological note. Donkeys travel on all fours, they are known to be stupid, and their nostrils are enormous. "Wonky" is slang for ketamine, and it rhymes with "donkey." Although ketamine is commonly used as a human anesthetic, urban legend labels it a horse tranquilizer, and horses are just one step removed from donkeys. "Horse" is also slang for "heroin," a much nastier anesthetic of abuse. None of this is coincidence.
After just 280 milligrams of insufflated donkey dust, Arctor staggered about on all fours like a drunken burro.
Donkeying is not pretty, but it's hilarious to behold.