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
Get the mug
Get a fuck knows when mug for your daughter-in-law Julia.