Fantasy is intersubjective. It is only produced by the interaction between subjects. However specific a fantasy may be to an individual, the fantasy itself is always a product of an intersubjective situation. It is a mask of the inconsistency in the big Other.-Tony Meyers, "Slavoj Zizek"
When we submit to the big Other, we sacrifice direct access to our bodies and, instead, are condemned to an indirect relation with it via the medium of language.. So whereas before we enter into language we are what Zizek terms "pathological" subjects (the subject that he notated by the figure 'S') after we are immersed in language we are what he refers to as 'barred' subjects (the empty subject he notates with the figure $). What is barred from the barred subject is preceisely the body as materialization, or incarnation, of enjoyment. Material enjoyment is strictly at odds with, or heterogeneous to, the immaterial order of the Signifier.
In order for the subject to enter the Symbolic Order, then, the Real of enjoyment or jouissance has to be evacuated from it. Which is another way of saying that the advent of the symbol entails 'the murder of the thing'.
What the fantasy of a sexual scenario conceals is the impossibility of a sexual relationship. It covers up the lack in the big Other, the missing jouissance.
Zizek avers that fantasy is a way for subjects to organize their jouissance - it is a way to manage or domesticate the traumatic loss of the enjoyment which cannot be Symbolized.