Top Definition
To exclaim that you don't know when an incident will happen.
Wife: When are you comming home?
Husband: Well I've got all this paperwork to do. I won't be back till fuck knows when.

Neighbour: Oh, you're looking for Steve? He's gone on holiday, won't be back until fuck knows when.
by Tom_NZ May 01, 2007
5 Words related to fuck knows when

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