Hmmm...so it just sort of 'appeared' in the slang and is now common. I can at least imagine the way 'restroom' (now a single word) was started....though I'm not sure WHY the almost-as-common 'bathroom' got added. I suppose because it was usually the same room. Now, people's ears just seem to expect those 'genteel' words instead of 'toilet'. I also hear 'facilities' or 'john'...and a few others, depending on what part of the country.