The answer lies in geography: People in the USA use 'restroom', 'bathroom' (but do not use toilet, lavatory) People in the UK use 'toilet', 'lavatory', 'WC' is used on signs only - you do not say "Where are the WC's" Other, slang words, are 'loo' (British), dunny (Australia), 'bog' (British)...

Nothing. They're all full of shit.

I live in London, UK, and most of the time I say "loo". This is the correct and polite word to use in most situations here, whether referring to a loo at home or to one in a public place. I rarely use "toilet" unless I'm referring to the actual toilet bowl. This term is actually considered by many people here to be a little crude. It does depend on your background and location though. If I'm drinking with the boys, then I could use all manner of words, mostly slang or crude terms, but you probably won't need to know any of those.

what a wonderful bouquet you have!

wc , restroom, bathroom, toilet and lavatory are synonyms