Well, there's a lot of opinion about military traditions without much fact.

FACT: Male soldiers of Highland or Kilted Regiments entitled to wear the kilt in uniform, do so without underwear. The gender of the monarch on the throne has exactly no bearing on this matter. It's as simple as that. Directions from the Adjutant and Regimental Sergeant Major make that quite clear, even if certain written dress regulations avoid the issue. Female soldiers of Highland or Kilted Regiments entitled to wear the kilt do so with underwear for obvious hygiene reasons.

What some Regiments did, or didn't, do while in the trenches in WWI, or what someone may have done when it was really cold, has nothing to do with the actual dress regulations. What soldiers wear, or don't wear, when they're tactical doesn't change the garrison and parade square rules. It's great history, but it changes nothing about the dress code.

FACT: There is exactly no rule saying that a Sgian Dubh has to draw blood before it can be re-sheathed. That's just a silly story that keeps circulating to try and keep young Squaddies from being stupid and waving their wee knives around.

For the record, I did indeed serve in a Highland Regiment.