Janken is arguably the most popular in Japan, beyond baseball and sumo.  This is the first game children learn in Japan so you should never have to explain this game, hopefully.

The Janken chant is, "Saisho gu janken pon," which basically translates as, "When Janken is played, it starts with rock."  The short version to this chant is, "janken pon."  Hint: if you want to psych out your students, say "Saisho kara," which translates as, "Let's play, NOW!"

3+ person Janken- this version of Janken can be confusing to understand because it is usually played extremely fast.  However, the concept is simple.  With three or more players, you keep playing Janken until only two objects are played.  For example, in a 4-person Janken, if two people play a 'rock,' one person throws 'paper' and the last person throws 'scissors,' they all must play again.  However, if two people play 'rock' and the other two play 'scissors,' the rock-players win.

Large group Janken- this variation of Janken is played by one person, the organizer, play Janken against the crowd.  This variation is most commonly used when there are many people playing (6+) and you want to cut the number of people down quickly. Anyone who beats the organizer keeps playing; the 'losers' and 'tiers' both lose.  The winners keep playing against the organizer until the group is cut down to a managable size to play amongst themselves.  Amazingly, Japanese are quite honest when this game is played in large groups, even if they are perfect strangers.

Janken can be used for practically any topic.  If the target vocabulary is actions, the winner tells the loser to do an action.  If the target is numbers, the winner can say a number and the loser must count up to that number.  If the target is food, the winner can say a color and the loser has to choose type of food that has the same color.  If the target is animals, teach the students the sounds along with the animals, have have the winner say an animal and the loser must say the sound.  Think about it and get creative!