1. An expression of indifference, apathy, or nonchalance. "Frig" here is a euphemistic, though still mildly vulgar, substitution for "fuck." You know what, frig it, I'm tired of waiting; let's go home.
2. An exclamation of dismay, exasperation, anger, or frustration. Ah, frig it! I can't find my keys anywhere!
See also: frig