Never! It's not unhygienic (unless you're hitching the kilt up over your arse to sit down), and your spurren covers your twig and berries! Some PC fucktard has his panties in a knot and should bugger off. It takes a real man to wear a kilt and the pilock that suggested this will probably want us all to wear thongs next! Geez.

I didn't do wear pants under my kilt at my wedding, I'm not about to start now!