But what a good game! Not only is it good throwing exercise (getting ready for baseball, I presume), but look at the attention it gets him! What a rise out of Mama! What a feeling of power!
You'll have to make this game less fun by not being part of it. Next time he throws his cup, don't play by his rules. Just take it away, put it in the fridge (or the dishwasher or anywhere out of sight), and make NO response, verbal or emotional. He may very well beg to have it back, and then you'll say - in a cheerful, firm voice - "No - game's over when you throw."
He won't go hungry (or thirsty)! I don't know what the general thinking is on this, but I'd consider giving him a baby bottle for his drinks the rest of the day - something a step down from his mature, two-year-old status. You may have a better idea about this.
And he'll probably test you several times. If you decide to give him another chance with the sippy cup tomorrow, and he throws it again, do the same thing. If he decides to throw something else instead, do the same thing as with the cup. No emotion, no lecturing, just a few brief, firm, friendly words when necessary. That needs to be YOUR game. (Since you're the Mama you get to play your own.) After a while he'll decide it isn't that interesting after all... and find something else to try on you. Gotta love toddlers!
(If he needs something to throw, get him a ball for outside. No Major League player ever made a team by throwing sippy cups.)