I think I am going to prank this really annoying guy who has had a crush on me for a while.
How much does he like you on a scale from 1 to 10?
His feelings sum up to about 0.5
If the prank is harmless, then got at it. If he really likes you, then he'd be a good sport about it.
I'm not interested in that. I plan to drain his bank account and die a horrible death so it will feel like an assassination to him.
Well killing him is not necessarily a prank, instead that would be murder. You are better off going with a more lighthearted prank where nobody is actually getting hurt.