Two Telling comments? The Answer Perhaps?

[Calgacus]

I think Jock pretty much has it right, though I'd say it's not necessarily about looking like a tourist, it's slightly wider than that. I think it's about needing a reason.

The 'uniform' of the average Scot is pretty much the same as the rest of the world. T-shirt, blue jeans, trainers (sneakers) and given our climate, some form of sweater or jacket. Now if you ask me, none of that is particularly elegant or even comfortable, but it is safe. If you dress like that, you will not stand out. You will look like everyone else on the street or on the television. You don't have to think much about it, it's all readily available, and it's cheap (or expensive, if that's your preference).

Where I live, there are few tourists so a kilt wearer would probably not be taken for one, but an assumption would be made that there was a reason for them wearing a kilt. Common reasons might be as follows:-

They are attending an event such as a wedding, Burns supper, ceilidh, Highland Gathering, formal dinner, etc.
They are a member of a pipe band.
They are celebrating a sporting event.
They are making a cultural/political statement ("I'm a proud Scot").
They are mildly eccentric.

One might well get asked 'Why are you wearing a kilt?', but one is unlikely to get asked 'Why are you wearing jeans?'. One can see how, outside of the highlands at least, there is some justification in this. The kilt is not the traditional garb of the lowlander so if the kilt is worn it is generally for some sort of reason, and most likely one of those I listed above. Within the highlands, less so, though not much less so. I have seen the very occasional highlander in a kilt who looked genuinely like he was an everyday wearer, and I have known only one lowlander who was (and still is) an everyday wearer.

In the more touristy areas such as Edinburgh, Glasgow, Inverness, Fort William, etc. I could see that not looking like a tourist would be a consideration. I would not wear my kilt as day wear in Edinburgh for example for that very reason.