I have a limited capacity for useless knowledge (I'm very efficient in that way) - so maybe that's why I feel obligated to share what I DO know.
I always thought the term "powder room" came from ladies powdering their noses in said room. But it actually originates from before then - when men wore wigs and put powder on them to make them less stinky. Gross.
I'm not going to cite a source on that one, but do a google search. It's true.