Quote Originally Posted by Tobus View Post
Yup, this is it. Though I would go a bit further and say it's more than convention. It sort of comes down to etiquette and manners. Just as wearing a Masonic ring would be unmannerly if you're not a Mason. Humans use clothing as symbols of who they are, and that's exactly what a clan tartan has been for about two centuries now, more or less. Even using a meaningless symbol like a Harley-Davidson logo on a t-shirt identifies you to others as someone who owns a Harley. If you display a symbol that has meaning to a group, you are (intentionally or not) telling others you're a part of that group. If it turns out that you're not a part of that group, some people take it as a breach of convention or a breach of etiquette.

The origin of "clan tartans" was a bit dubious, and obviously contrived, but it nonetheless exists today and has a fairly long tradition. You may wear whatever tartan you choose, but some will frown on it. You may not know they're frowning, or you may not care even if you did know. Make your choice based on whether it bothers you that others will be bothered by it. If you find that you don't care what they think, then wear whatever you like. No one will arrest you for it.
In a nutshell sir. Well said.