In the 80s, Konami of America and Japan released many games for the Nintendo Entertainment System. Traditionally, programmers would program in hidden 'cheat codes' to help make gameplay easier, which aided especially during late testing periods before commercial launch.
Konami released many popular games on the NES during this era, such as Gradius, Life Force, and Contra. These titles, as well as many subsequent ones, used the same cheat code listed above. Because of it's reoccurence, it became known as 'The Konami Code', and knowing it by heart is one of the trademark signs of a true, old-school gamer.
A common alteration on this code is:
Up-Up-Down-Down-Left-Right-Left-Right, B, A, SELECT, Start.
Many people mentally add in a 'select' in there for one reason only--on the menu screen, pressing select changed the cursor to '2 players' instead of '1 player'. Contra was always more fun to play with a friend.
guy #2: You pussy!