No hard-and-fast rules…I’ve known true Scottish men who choose to wear their girlfriend’s tartan, or that of their mother’s family, simple because their own one is hideously garish.
I have a Muted Dress Stewart tartan kilt that I used to wear to Renaissance Faires. Actually a remote ancestor was a Kirkpatrick, which I’ve found is a clan associated with the Colquhouns. I’d like to get a kilt with the Colquhoun tartan, but kilts are nearly three times the price I paid for mine in the early-'80s.
And I’d like a Utilikilt.
Since you are of some Irish decent, you can joinClan Cian. They have their own tartan.
I’ve got mostly Johnstone with some Robertson as well.
Our hunting plaids are nicer than our dress plaids, in my opinion. My brother usually wears an ancient Robertson hunting.
Check us out! We were some badasses! 
Robertsons
Makes me want to get all dressed up and kick somebody’s ass! 
What the hell?!? Bill Gates sabotaged my friggin’ links!
Ignore the links above, I have no idea what the hell happened…
Fixed the links.
Now, I have this green and blue plaid tie I like a lot. And reading this thread, I got to wondering whether it was a legitimate tartan or just something some foof at The Gap drew up.
It turned out to be Ogilvie of Inverquharity, Inverquharity being some 15th-century heap of stones in Angus, in the east-central of the country.
Now I have no idea whether this means anything, but I am related to some Richardsons 4 generations back. And on one of those “find-your-clan” websites, Richardson was listed as one of the septs of the (an?) Ogilvie clan. So I have a cover story which will enable me to wear my tie.
I used to know of a website that listed Irish tartans and such. I know that some of my family came from Cork, and I believe my father mentioned that some of them came from Killarney, or around that area.
Failing that, how about a Cornish kilt (plain black), or one of the Cornish tartans?
http://www.alanrichards.org/cornishtartan.htm
It doubt there’s any problem for the bride to wear the groom’s tartan or vice-versa. I recently attended a wedding where the majority of us wore kilts and the groom worked in a part of the ceremony where he pinned a scarf of his tartan onto his bride’s wedding dress right after the “I do” as a “welcome to the clan.”
Ah, good. I opened this thread after reading the title and thinking “WTF??!! How dare he? And after last Tuesday night, too!” But I see alll is still right with the world, and I will now expect pics of “NCB in kilts” in my private email sometime this afternoon, you know the one, or I will post the bunny pic costume.
Erm. “Bunny costume pic.”
That is all.