To remove a muck sack by unsticking one's balls from the inside of one's legs. This is generally done by hand or by spreading the legs, and is widely regarded as one of the best feelings in the world.
Person 1: Wow I feel amazing!
Person 2: Why?
Person 1: I just shillacked one of the strongest muck sacks of my life.
Person 2: Why?
Person 1: I just shillacked one of the strongest muck sacks of my life.
by alfbon February 7, 2018
Someone who takes large objects up the pooper then sucks them clean. Then meets up with a Diehl for some afternoon delight that involves whips, a Sigfreid and Roy DVD, three gerbles, his mothers undies, taco meat, a nine iron and 3 pills of valium which he uses as a supository for euphoric effects around the anus area. A Shillack has never gotten a boner from a girl... ever. The only thing that gets a shillack off are Chippendale dancers and pictures of Lance Bass.
Last time I invited a shillack over, my valium perscription was missing and he was wearing his moms panties on his head.
by The Great Z-Dubb October 22, 2008
Ex. 1: We were shillackin in the mornin' before class watching Sportscenter and eating Captain Crunch.
by jtruongie February 17, 2005
Hillary really took a shillacking in the election. I guess that $6 million she paid to astroturf Reddit and start fights at Trump rallies didn't pay off?
by ColonelCluster November 9, 2016