Father-in-law Jack's term for son-in-law Gaylord "Greg" Focker in the new "Little Fockers" movie starring Ben Stiller and Robert DeNiro.
Jack's use of the term stems from his realization that Greg, who now has 5-year old twins with his daughter Pam, is next in line to be the Byrnes-Focker family patriarch.
Usually an interjection. The word itself can have many literal meanings, however, based on your standpoint on matters of religion or diety. The 'God Cock', per se, could either be,for example, Absolutley massive, on a godly scale, to non-existent from an atheistic viewpoint.
God Cock! My testicles are perspiring. Marc, wipe them for me.