National Dress or Costume.

[mongers]

Hey, this topic seems to be a gift that keeps on giving, just google your nations "national costume". 

Here's GB's 2010 Miss Universe get up: 

[Razgovory]

National Dress for the Brits

[Scipio]

I don't think a MEEEEShegan sweatshirt over khakis is national dress.  But it ought to be.

Or a Georgetown lapel pin on your navy blue pinstripe suit.

[Barrister]

Flannel and a toucque.  I've worn it.

[dps]

I don't own a cowboy hat or boots if that's what you mean.

I don't know, I figure the nature of an American national dress would be as problematic at it is to a Brit.

Jeans, tennis shoes and a t-shirt.  Sure, I've worn that.

And the national costume of England, btw, is the 3-pc pinstripe business suit.

[Tonitrus]

Flannel and a toucque.  I've worn it.

After the Mountie, I was going to go with...

[Neil]

The English-speaking peoples don't have a national costume, because all clcothing and fashion belongs to us anyways.

[Sheilbh]

I've worn a full kilt.

[Darth Wagtaros]

A gun?

[mongers]

An alternate Cal approved costume ?

[jimmy olsen]

Thank God my parents chose this tradition, and not the other Korean tradition of taking your new born son down to the photo studio to have a beautiful airbrushed spreadeagle portrait taken of his pecker to blow up, frame, and display in the living room.

Photo studios in Korea will put these gigantic pecker shots in their window displays to show off their artistic prowess and attract more business.

WTF? I've never heard of anything like that.

[MadBurgerMaker]

I've got a pair of busted up old square toed Ariats, which with jeans and a t-shirt are about as close as I've come to anything like 'regional dress.'  Cowboy hats aren't my thing. Sunglasses work just fine.

[CountDeMoney]

I don't own a cowboy hat or boots if that's what you mean.

I don't know, I figure the nature of an American national dress would be as problematic at it is to a Brit.

Both are variants of the standard business suit:  the Brit banker and American bidnessman.

[Syt]

Schleswig-Holstein doesn't seem to have rigidly defined national costumes or "Tracht" as it's called in German for males, so I'll go with the shanty choir look (worn with white or black pants):





Haven't worn it, though. Still, I keep that option open in case I ever get invited to a Tracht-themed fest, as Austrians are rather fond of those.

[Barrister]

Slightly more seriously, I did wear a Ukrainian shirt for folklorama one year in Winnipeg.  I volunteered together with my Ukrainian girlfriend.

Something like this.