I first presented this “U”-phemism–first cited by the OED, appropriately, in a 1940 Nancy Mitford quote–as a Portland, Oregon, outlier, but I now believe it’s made the grade as a NOOB. The Google Ngram chart, below, shows a more than 50 percent increase in U.S. use between 200o and 2008:
Then there are these recent quotes:
I saw Another Happy Day, and thought you really brought it home playing the bitch ex stripper, coke-whore mom — nearly spitting nails with every word catapulted at your co-star, Ellen Barkin. That cat fight in the loo alone was worth the price of admission (“An Oscar-Themed Open Letter to Demi Moore,” Huffington Post, February 28, 2102)
SUSPECTED PEEPING TOM HITS CAMPUS LOO (Coast Report Online, Costa Mesa, Cal., February 21, 2012)
…it’s no longer the morning news that dad is reading on the loo, but rather a tablet computer. (Consumer Reports.org, February 17, 2012)
I can’t top that, so, like George Costanza and Mitt Romney, I will just say:
Gotta go!
No pun intended.
notoneoffbritishisms.com 
Loo is a great word. It doesn’t have the uptightness of “restroom”, the bluntness of “bathroom” nor the old-fashioned awkwardness of the “ladies” or “gents”. You can say it without blushing because it doesn’t actually conjure up images of what’s actually done there. And most importantly, it flows out of the mouth nicely. Looooo.
I think I saw a “loo” in this morning’s Phila Inquirer. I will not add anything political as to what the Inquirer could be used for in the loo.
I’ve been using it for years, and lthough it may be a false etymology, I like to think it refers to Waterloo, where Napoleon got his comeupance.
It’s also worth mentioning that “loo” is generally a word used by women. If a man used it in most British pubs, as in “Erm, excuse me but where’s the loo?”, he would receive some strange looks. British men tend to express their needs in more action-oriented ways as in “Right, I’m dying for a piss, keep an eye on me pint, will you?” or “I gotta go and point Percy at the porcelain, won’t be a tick.” Or they use the noun “bog” or any other of many choices. Say “I’m just nippin’ to the bog, Be right back, lads,” and you could be mistaken for a true Brit.
“Bog” is a wonderful one, and quite descriptive, too. I particularly like “staff bog,” which I haven’t seen in the US yet. The staff bog is a little narstier than the guest loo.
I think you might be right there. A lot of my male friends here in the UK have a tendency of saying “I need to go for a pee”. Straight to the point, but not exactly what I want to hear.
Today’s NY Times crossword (3/2/12): Place to go in Soho = LOO. It’s becoming epidemic!
Haints, I don’t know who you’re mixing with but “pee” and “wee” are words used by children and laydees, never amongst men. Looks like you are female from your pic. Maybe the blokes are just being twee in your company?
You lot are priceless. I am now officially on the lookout for “bog.”
@Rusty Git – anything is possible. pee + wee = twee? @Ben – have you done a post on “you lot” yet?
I am waiting–WAITING–for its first appearance here.
I reiterate my warning about “bog” – it is a vulgar expression in Britain, and could lead to unfavourable judgements from “polite” society. I’ve heard “loo” frequently used by men (though perhaps not down the boozer or at a football match), especially when talking to women, while “toilet” – a slightly harsher euphemism – is fairly universal.
Interesting that the first quote in the OED is in fact by James Joyce, using not only its supposed full form (“Waterloo”) but also its shortened one as a pun from French: “loup”.
Interesting, David. So, in an unfamiliar pub, what would the average “nice” Englishman ask for if he need to find the loo/bog/toilet? Would it matter what sort of neighborhood the pub was in or what sort of crowd it drew?
You can’t go wrong with “Where are the toilets?” though when I frequented dodgy East End pubs I used to ask “Where’s the gents’?” “The loo” is what you’d ask for in tea rooms and so forth, or in female company. Usage still seems to vary across the country, but the good thing about “loo” is that it seems to be replacing (or has replaced) ridiculous euphemisms such as “Where can I wash my hands?” “I’m going to see a man about a dog” and “I’m going to spend a penny”.
When I was at school – where the only name for it was “bog” – we took great delight in “I’m going to point Percy at the porcelain” and “I’m going to shake hands with the wife’s best friend”, faux Australianisms from The Adventures of Barry McKenzie comic strip.