From Wiktionary, the free dictionary
From хуй (xuj) in reverse.
йух • (jux) m inan (indeclinable)
- (minced oath) dick (euphemism for хуй)
Осенью, все птицы летят на йух.- Osenʹju, vse pticy letjat na jux.
- In autumn, all the birds fly south/go to hell.
- errative for юг