Saying the opposite of what you mean is…
The audience knows the Titanic is going to sink but the actors get on the ship anyway.
There is a "No Smoking" sign in the break room for the employees at the cigarette factory.
When something happens that is the opposite of what you think will happen...
"Sure, I want to go hiking in the mountains...with a broken leg"
Snow White ate the apple the old woman gave her.
When asked a question, for the seventh time, the teacher said, "Sure, I don't think I've answered that one enough times yet".
The men are taking an escaltor to the gym.
In a scary movie, the character goes into a house they think is empty, but the audience knows the killer is in the house.