I just learned yesterday (on Howard Stern's show) that Jonah Falcon has the world's largest (recorded) penis. 9" flaccid and 13.5" at other times of the day. Not sure why I felt compelled to post that...oh, wait. You mentioned giant cock. Welcome!
What happens? Fire and brimstone coming down from the skies. Rivers and seas boiling. Forty years of darkness. Earthquakes, volcanoes...The dead rising from the grave. Human sacrifice, dogs and cats living together - mass hysteria. You know, run of the mill standard type stuff.