"Fasten your seatbelts. It's going to be a bumpy night."

Can any one tell me the meaning and origin of "Fasten your seatbelts. It's going to be a bumpy night."?

Thanks
Hry

It's from a movie, All About Eve .

Margo Channing (Bette Davis): Fasten your seatbelts, it's going to be a bumpy night

She said it at the beginning of a party. There were a lot of undercurrents. A lot going on between people at the party.