I have a couple thoughts on this thread so far. First I will address the tartan ties.

As others have mentioned, the tartan tie is not an "unforgivable sin" but is not very traditional. I have seen pictures of highland chiefs wearing tartan neckties but those pictures tend to be from highland events and they are a bit "costumed up" with bonnets, plaids, and cromachs. In short, they are going all out for the event and it certainly should not be taken to reflect what they would consider normal day wear.

Now, it being traditional may or may not matter to you. It's simply something to be aware of. If wearing the kilt outside of the highland tradition, I think the next serious consideration is simply whether or not it looks good. That is subjective, of course but it's worth considering. Liam looks good in his photo so perhaps it's the particular tartan as well. McMurdo has a tartan suit that also looks really nice but I don't think it'd look as good with, say, the "loud McLeod" tartan. My kilt is in MacDonald modern and is fairly dark green and blue and very bright red, I don't think it'd look good with a matching tie.

The other thing I'd like to address is the picture of Sean Connery. I like the man as an actor and he was the best James Bond but a fashion icon he is not (remember, in Bond he was dressed by a costumer). You don't wear a long tie with a tuxedo, why would you wear one with prince charlie? Celebrities are notoriously bad at dressing themselves. Look at any number of black or white tie events for actors or musicians, the fashion blogs love to point out all the poor choices they make. This applies to saxon wear in most cases but most photos I see of Scottish celebrities in kilts fall into the same trap of looking like they rented for a highschool prom.

It goes back to the idea that to break the rules, you first need to know them. That's the difference between someone who is a trendsetter and someone who is just ignorant. I think that if Mr. Connery had made the purposeful decision to wear a tartan bow tie or vest, he would have looked much better if still not traditional. The long tie with the short vest makes me suspect that he just asked for whatever tartan neckwear they offered at the rental shop.

And I doubt he was born knowing how to wear a kilt any more than he was born knowing how to distill whisky. It may be national dress but if he didn’t grow up wearing it (which our resident Highlanders say is common) there’s no reason to think he knows better how to wear it than anyone outwith Scotland, especially on this forum.