Video taken from the 2008 RPS championships in Las Vegas
The Rules (As taken from the USARPS league)
The Basics
Rock Paper Scissors is played between two players - male or female, young or old, slutty or prude. It’s an equal opportunity sport. No equipment is necessary, though some players prefer to wear "throwing gloves" for maximum comfort and intimidation. All you need is an arm, and a wrist, and fingers. It is best to wear loose fitting clothes, and pre-game stretching and manicures are strongly encouraged.
The Throws
There are three permissible "throws" in RPS: Rock, Paper and Scissors. Rock crushes scissors, scissors cuts paper, and paper covers rock. There are NO exceptions. When two players "shoot" the same throw, it is a stalemate and they must throw again.
A player who makes an illegal throw – including but not limited to "Hang Loose," "Westsi-ide," "Fire," "Water," "The Bird," "The Fonz," "Su-Fi," "Live Long and Prosper," "Texas Longhorn," "This Big," or "I’ve Got Your Nose" – will lose a point and may be disqualified.
Rock can be thrown any way as long as the fist is clenched, as if you’re squeezing the life out of Stuart Little.
Scissors is formed with your index finger and middle finger extended and shaped like a "V". It can be thrown horizontally or vertically (Please note that international rules differ).
Paper is formed by extending all your fingers out, as if you’re about to slap your little brother. It is always delivered horizontally. Never vertically. Vertical paper is for hoodlums and misfits, and we don’t stand for it. Paper is traditionally thrown palm down, but may be delivered palm up, which is called "The Subpoena." Serving the subpoena is considered arrogant, but can be very effective when used properly.
The Action
The "Pump" consists of closing a fist, holding it out in front of your body with elbow bent at a 45 degree angle, and thrusting it up and down three times. (Please withhold any masturbation jokes until after your match.) This must be done IN SYNC with the opposing player. Players are allowed to chant "RO-SHAM-BO" to help get in sync. In fact, it is even encouraged.
The "Shoot" is when a player actually delivers the throw. It comes after the first three pumps. Players may follow shouting "RO-SHAM-BO" with "SHOOT." The delivery of the shoot must be in sync with the opponent. If the shoot or the pump is not in sync at any time, the referee may declare the action dead, or penalize the player at fault. Point is: be in sync. Seriously.
Each "engagement" begins with a referee raising his hand vertically between the two opponents and saying the word "engage!" (Please note: in international play, this is commonly stated as "en garde") The referee’s call cues the players to "pump." It can also be a clever time to propose to your girlfriend. If for some reason you don’t have a referee, it is up to the players to cue the action.
The Gameplay
Each throw is considered an "engagement." The best of three "engagements" is a "bout." The best of three "bouts" is a "match."
All referees’ calls are final. Instant replay has not yet been instituted in RPS. There is no post-match arbitration allowed, so deal with it, crybaby.