Русско-англо-русский юридический словарь

I'm English, and would probably use 'toilet' most of the time, and always in the context of a private home. Or I might use 'loo' which is more informal, but maybe outdated/whimsical.

Not sure myself exactly how it works, but anyone using 'lavatory' is probably related to the royal family, or wishes they were. But then 'lav' is somehow at the other end of the scale.

'Bathroom' is never used and is often found funny when used by Americans. So is their discomfort when you use 'toilet' in the US.

I might use Ladies and Gents in the context of a public facility/bar/restaurant - signage will often use these terms, although perhaps more often written Gentlemen. Actually, thinking about it, I'd always use Gents in a pub, possibly there's a need to reinforce one's own gender identity!

I can't think I've ever heard WC, but I've seen it used on architects' drawings, probably for reasons of space. (English Language & Usage Stack Exchange)