Bai in its origin is probably from Gujarat and equal to respected lady. Same is the case with Mai (used in Sindh and Punjab), probably its root is Maa (mother).
But these both words are not considered good outside these regions. Bai because of Red-Light areas and Mai is considered as someone illiterate.
Have you hear someone still using these words for referring to gentleman ladies ( heard this term in a classic show Sach Gup).
Not necessarily. If someone wants to ask me something, they can use any of the following ways.
Aik na aunty (listen aunty)
Aik na tai (listen sister)
Aik na Maushee (listen mausi)
Aik na bai (listen lady). I personally feel no bond at all with a person when they talk to me like this way...although its not literally offensive in Marathi, I dont prefer to be addressed this way.