Disregarding the amusement from the game you might get, why waste time when attempting to go through a door. The rest of the class might be annoyed at waiting while you decide who goes through the door first...
When we started to do rock-paper-scissors, the process became really quick - about two seconds to notice the situation, exchange the looks, shake our fists three times and show rock/paper/scissor. Sometimes it took a bit longer if there was a tie in the first round - but never long enough for anyone else to be bothered.
