What do you think about me having fired a giant spit ball at the dude in the front of the class?
That is wrong and inappropriate. Did you think it would be funny?
Not really, I don't like him and I was just bored. I figured you would ask me what that sound was as well.
Not liking someone is fine but that's no excuse for shooting a spit ball at him. Theres no reason to make his life worse and risk getting yourself in trouble when you could just ignore him and move on.
It's just water, it won't do damage to him.
It's rude and disgusting to shoot a spitball at someone. You should never go out of your way to make someone feel uncomfortable. Consider how you would feel if someone did that to someone you care about.