I wear what suits me.

And if I really need a reason besides the fact that the tartan either
1.really looks great or
2. can be had at a steal or
3. I'm in the mood for it,

then I can probably think up something like somebody married to my great-aunt Sue who knew a guy from Hoboken who visited (fill in the blank here) during a trip to Scotland one time.

Shoot, nearly everybody has Celtic blood they can't even indentify exactly. One thing about our Scot and Irish forebears: they were quite prolific!