If I said, I wonder if you could tell me where I could spend a penny? What would you say?
Maybe I could ask for directions to the smallest room. No?
OK, I'll spit it out - Where's the loo? I'm desperate!
The loo? The toilet of course, but we don't use the word if we can help it. Still, Americans ask for the bathroom, so that's even more confusing.
Now, if you spend a penny, that's probably a number one; if you plan something more substantial, that's a number two or crudely put, a crap. You could be talking crap or say, 'that's a load of crap!' The origin being from a toilet manufacturer called Crapper! If you're interested in this little convenience called the WC, (water closet) here's a brief documentary.