Not sure where you're from, but the proper word is Restroom. Not Bathroom (a room with a bath) or Lavatory (a room with conveniences for washing and usually with one or more
toilets).
I hate it when people use all those jargon/nicknames for these places.
Lol,
lavatory is neither jargon nor a nickname, you angry semi-literate twerp, whereas restroom is far more recently adopted euphemism for the lavatory.
Lavatory was and is a not uncommonly used name for the "room" in
both America and England, albeit it one which has fallen somewhat out of favor on this side of the Atlantic since the 1950's.
By the outline of your own argument, a lavatory,
by your own stated definition "a room with conveniences for washing and usually with one or more
toilets" fits far better than the weak-assed euphemism restroom . . . unless you are in the habit of nipping into the little boy's room for your siestas.
I don't mind your untutored pinhead ignorance all
that much. Just shut the fuck up, and don't mistakenly impose it on others.
Consider this your learning experience: