fuck knows

as far as one knows

To the best of one's knowledge, as far as someone knows or possible information to be gathered about the topic, subject, aspect, or situation.

fuck if I know

I have no idea whatsoever

fuck it

An expression of great indifference or nonchalance.

fuck off

To go to hell; to disappear or go away; to screw oneself.

fuck someone upside down

To give someone a bad scolding.

fuck someone's brains out

To sexually penetrate (or be penetrated) in a vigorous but pleasurable manner.

fuck this

A dismissive expression of great indifference or nonchalance.

fuck with

To interact with in a careless or inappropriate way.