Have everyone line up, show them all 7 different coloured scarves or bandanas, each one is a colour of the rainbow. Now blindfold each player in turn with one of the scarves and mix them all up. The players must now arrange themselves into the colour order of the rainbow. For a joke, give them all the same colour blindfold (you would have to blindfold them first) then whisper the blindfold's colour into their ear. See how long they take to realise they all have the same colour blindfold.
Source: From the original site.(Submitted by: Pat)