It is a polite way of swearing. Used inserted into a sentence, when pronounced sounds like a common curse word. However written out, it looks like an innocent mistake at first glance.
This show is Sofa-king stupid.
That is Sofa-king awesome.
Deriving from ‘Sofa King’, a play on "so fucking", sofa-king is to be used as an adjective-modifying adjective.
I am sofa-king tired right now.