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.
As a gerund or modifier: This is God-cocking bullshit.