Quoted from TheLaw:Exactly....it's "Whom's back" for fuck sakes.
Negatory. Who is a subject, whom is an object. Who is back? is grammatically correct because who is the subject of the sentence. You would use whom for things like, "This is for whom?" or "To whom am I speaking?"
And it would be "for Fuck's sake." FYI It is Fuck whose sake we are bemoaning.