What is it called when you use "I would do X" to show strength of feeling? [duplicate]

Like:

"Sam and Lilly hate each other now. Their relationship is spiraling to an end." "It is," she said, and she spoke like a fortune teller that made my previous _________ about their fall true.

Hyperbole is defined as

exaggerated statements or claims not meant to be taken literally.

Given that hyperbole is very often comical, this word pretty much fits the title of your question perfectly.

Your example sentence is rendered:

She spoke like a fortune teller that made my previous hyperbole true.

NOTE: "spiraling to an end" is not a particularly good example of hyperbole. Rather it is a metaphor. If it was a particularly exaggerated metaphor, it would be a good example of hyperbole, but it isn't. If anything, it's mild hyperbole.

A strong example of hyperbole is:

Sam and Lilly hate each other now. They hate each other so much that Sam would guillotine off Lilly's head without batting an eye, and Lilly would push Sam off a five-thousand and sixty-seven story building without a second thought.