Of course, it is generally understood that you chaps and chapesses over on that side of the pond are a little more sensitive to these matters than we tend to be over here.

In all my 54 years of kilt wearing and with my life-long interest in Scottish Country Dancing (which is also set dancing) and Highland Dancing (which is not), the unspoken rule on this (and the one I have followed) is:

Social dancing: underwear is not really required since, if your dancing is under control, you will not be in much danger of revealing anything. If your dancing is of the wild, Ceilidh type - or "Reeling" as it is sometimes known nowadays - then the wearing of underwear might be advisable. Although, it has to be said that, one of the joys for experienced dancers is the giving of little extra 'flicks' to the pleats at certain points in the dance or when executing certain footwork - done just to 'tantalise' those watching - especially if one IS dressed regimentally!!

Exhibition, Display or Competitive dancing: Underwear should be worn since some members of your audience might be sitting on the floor, or you might be performing on a raised stage or platform, and they will have a better view!

Whatever underwear you choose it should NOT be of the Boxer variety (looks too like old-fashioned knickers) nor, under any circumstances, should it be white. Black, bottle green or navy blue briefs would be fine. In one exhibition team I danced with years ago, all the men had to wear flesh-coloured briefs so that members of the audience never knew for sure what they might have seen!!

I'm not advocating this one but, also years ago, one of the guys in another team had a complete pair of briefs tattooed onto the relevant part of his body - in a representation of his Clan tartan!!!
He never needed to wear underwear!