In South America, people use WC, Patent (because it was written on the loo), or just Water (in Uruguay, at least) a lot. So it would be funny if (at least WC) was not as known in the English-speaking world. Patente (used in Brazil) is obviously just derived from the Patent label.
According to my grandfather, when he was growing up poor in southern Illinois in the 1930s, "toilet" was a crude word and people said "W.C." to be polite. Outhouses were more common than toilets, to the extent that old-timers then thought it was disgusting to defecate in the same building where one slept. Perhaps "water closet" seemed an appropriately exotic term.
Here's a version, but I don't think my grandmother's relied on foreign language as a device: http://www.brinkmanonline.com/humor/church/wc.html