Kung Fu - originally known as Kung Fu Master in arcades - is one of the games that everyone has likely played at one point or another. Whether or not they understood what was going on while they played is another question entirely.
Kung Fu is a fairly simple side-scrolling action game in which the player tries to reach the end of the level without getting beat up by hordes of kung fu fighters, all in an attempt to save their girlfriend from the mysterious Mr. X. The game's difficulty is certainly nothing to laugh at, and it makes for a fun 2-player game if you feel like sharing the pain of losing over and over again.
Fun fact: the game was known as Spartan X in Japan, tying in the game with Jackie Chan's Wheels on Meals film that came out just a few months before Kung Fu Master in arcades.