Used sarcastically when you don't want something to happen or something bad already happened. Can be used interchangeably with "one would hope", "hopefully so" or "I'm hoping so". It occasionally can be used to express a neutral emotion as well, especially with a sense of indifference.
Jack: Bro, your girlfriend just cheated on you.
Elliot: I hope so.

Ivan: Janie, you just ran through three red lights!!
Janie: I hope so.
by probably_jenkins May 23, 2022