The plays of Neil LaBute, American theater's most prolific and astute chronicler of the really bad things men do to women, are sometimes marred by contrivance and a too-facile cynicism. But every once in a while he hits it on the nose, as in this astringent tale of the assorted entanglements of two working-class couples. The fine off-Broadway production directed by Terry Kinney (moving to Broadway early next year) struck a nice balance between LaBute's truth-telling and his moralism.