cajunscot, I think the issue has more to do with context in this case.

Going to a highland games or a ren faire in a kilt shirt with shorts/pants on strikes me as being similar to going to the symphony in one of those suit/tuxedo t-shirts.

Some people are going to see it as "talking the talk", but not "walking the walk". It may not be improper, but it's going to get some looks for various reasons.

I'm not passing judgment, just saying.