Which one to wear?

[Wareyin]

If you are wearing a tartan, be prepared to be asked if it is your family tartan. If not, you may (but not always) be asked why you are wearing it. I have one tartan that is not my family's, and I answered that I just wear it because I liked the pattern. Of course, once I got a family tartan, I only wear that one, anyway.

There are no rules, but people have an expectation (most especially non-kilted people) of why you wear a certain tartan. At least here, in the US. The social conventions may be different if you are elsewhere.