If you suddenly had "fuck you" money what would be the first thing you did?

Dump all of it into researching how to grow tardigrades larger, until they are big enough to take down a fully grown man. Then build up an army of them and unleash them on the world.

With my tardigrade army giving me complete control over the world, I will begin enacting my ultimate goal:

Making that bitch Sarah pay for making fun of me in primary school.

"Fuck you" Sarah.