Fuck Shack, any enclosed area or location, usually cramped in size, that is used for couple or group sex. (i.e. a car, port-o-potty)
We found your car with a note inside:

"Thanks for the F-Shack. - Dirty Mike and the Boyz"

There must have been some homeless guys foolin around in it. We call that a soup kitchen.
by Tsmudge09 October 8, 2010
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