in addition to the current yellow and red cards?
namely, the 'haircut' card.
to be used either on players who clearly spend more time at the salon than playing football (like this bloke) or on players who just desperately need a haircut (see here)
it would help the footballers concentrate on playing the game rather than tending to their tresses. could also be used in ice hockey.
(I should add that I have little interest in or understanding of the beautiful game, but do shout 'haircut card!' at the tv when I see a particularly good example of why men should not be allowed to choose their own hair style)