'Les toilettes' often cause problems for people visiting the city and locals alike. From my experiences taking groups of tourists around Paris, I can safely say that the shock for the great majority of Americans when they find out that a lot of toilets in France are unisex is one of the biggest shocks they encounter.
The greatest shock for me was the à la turque toilets, because you have to master the art of squatting, not losing your balance, or dropping anything out of your pockets and not getting your feet splashed when you flush! If you don't know what I'm referring to, then count your lucky stars... if you do, you can probably sympathise with me!
There's also the problem of being caught short in public. I've heard that it can cost you up to 5 euros if you pop into a café and ask to use their toilet!
In the past (again, during those tour guiding days) I've had to run into the McDonalds on the rue du Rivoli with a client and on one occasion, I took all 40 kids up to the top floor of BHV in order for them all to go.... (both freebies and well-worth remembering!) But without doubt, the worst situation for me was a boy getting diarrhoea whilst we were visiting the Arc de Triomphe - I had to make the split-second decision of whether he was bad enough that we ought to risk life and limb and try to cross l'Etoile at street level or if he could manage going down, under, up and round to the nearest toilet!
So today's useful piece of vocab: où sont les toilettes, s'il vous plait?
P.S. The video at the top of this post is funny, but it does also have a lot of truth behind it! Beware of any unidentified liquid on the pavement!