The alarm cock is a hilarious sexual prank. A man waits for a woman to go to sleep and retires to a seperate room to masturbate feverishly. Right before ejaculation he returns to the bedroom to cum right in his girls face. She will wake up during this and her confusion will quickly turn to outrage which will be responded to with a hasty retreat. The alarm cock maneuver has also been referred to as the graveyard glaze and the midnight jack.
The definition for Alarm Cock is self explanitory. If performing the alarm clock maneuver it is important to use catchy one liners before escaping. "You had it coming" or perhaps the Woody the Wood Pecker noise would suffice.