There are three categories of tartan a gentleman must recognize.

First, restricted. The Balmoral tartan is the alpha in this herd, to wear the Balmoral tartan you are supposed to have explicit permission from HM Elizabeth to even buy the cloth. Can you buy it and have a kilt made from it, probably. Would it be in extremely poor taste to do so, absolutely.

Next, respectful. Personally, I really like the MacLeod, the bright yellow one we have all seen, the MacLeods refer to it as "Loud MacLeod". Another one is the USMC leatherneck tartan. Can you buy it? Absolutely. Should you wear it if you aren't a US Marine or a MacLeod? It depends on which marine or MacLeod you ask.

Fianlly, the universal setts that anyone can wear, "no Scottish blood required as long as they have a bit of Scottish in their heart." This is an enormous category. Black Watch, the many and various Stewart setts, it goes on and on.

Another avenue of exploration would be the regional and district tartans. If you hail from North or South Carolina, or can build a legitimate connection the Carolina tartan is really quite fetching. I must admit as an alum of UNC-CH I am a bit stuck on ordering a red kilt in my clan red or the Carolina. Heaven help you if you a Clemson alum of course ;-)

If you choose a clan tartan to which you have no genetic connection, do your hoemwork. You might someday meet soemone who might take umbrage. If you can trot out, "I bought this one because it is the prettiest sett in the entire registry," you'll likely get away with it, it might be even better to be able to say, "I really admire/ respect/ connect with the clan chief's achievements/ efforts/ push towards high quality sheep/ art museums/ green energy" Or something.

In general if you are wearing it respectfully it will probably be OK. Except for the Balmoral. Her Majesty will send you a personal git of your own to hound you day and night until you send the item back. And really a gentleman would never do that anyway. While you are shopping learn to recognize the Balmoral and if you ever see someone wearing it, know what you are seeing.