My parents were Eastenders (cockney, east London) and there are loads of terms they and their neighbours used eg Kermit = road (frog and toad). A word I have noticed that seems to have recently had a wider resurgence lately is taters = cold (taters in the mould - potatoes in the ground).
In Mexican Spanish (not sure about other countries) when you say “Aguas” which means “Waters” it’s like saying “watch out.” Originates from when people would toss out their dirty water or chamber pots out second story windows to the street 
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I heard that the English expression “loo” for toilet is a corruption of French “Gardez l’eau”, from the warning before dumping a chamber pot out a window.
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Oh, wow! No kidding.
That’s interesting, I hadn’t heard that before. I read a different explanation - in hotels/inns the toilet on the first floor was always room one hundred - 100. 