I did raise the point in the FAQ section and got a quick reply..

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Trefor Heywood (11:00:04) :

And what pray do kilts have to do with pants? For many kilt wearers this would be an ideal opportunity to celebrate a day off from trouser tyranny!
21 03 2007
Roy (11:03:05) :

Trefor,

The good news is that this is a holiday, and as such, no one owns it. So celebrate in whatever way you see fit. And tell your friends."

So we can see fit to wear a kilt!