What type of computer, laptop or desktop.
And why, is it for some sort of insurance claim ?
For a laptop you could try dropping it, maybe on a marble floor (I did this about 7 years ago at an airport with my company laptop. Case cracked and whole thing was replaced).
For a desktop, not so easy.
The inside of a desktop case is mostly air with just a few small parts. I would have though pouring a liquid like coke onto the electronic parts inside would kill it.
Or get an electrical power surge to go through it. Try putting it outside when it is raining and hope it is hit by lightning.
Or drive a vehicle over it.
Mind you , I am not sure why I am helping you wreck a computer as it sounds as though you are up to no good !!