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English word fart sack comes from English fart
fart (English)
(colloquial, usually, as "fart around") To waste time with idle and inconsequential tasks; to go about one's activities in a lackadaisical manner; to be lazy or over-relaxed in one's manner or bearing.. (informal, mildly, vulgar) To emit digestive gases from the anus; to flatulate. (colloquial, vulgar) An irritating person; a fool.. (colloquial, vulgar, potentially offensive) (usually as [...]
fart sack (English)
(military, slang, vulgar) A sleeping bag (especially a heavily-insulated bag).