The first, but even that is lacking in cruelness. The second one is more like, I can't wait for you to die, while the first one is oh, you died. Not like I care.
The first one is like I will not be my happiest until the day you die. The second is indifferent.
I am nothing but a mouthful of 'sorry's, half-hearted apologies that roll of my tongue, smoothquick, like 'r's or maybe like pocket candy that's just a bit too sweet.
"The day you die will be the happiest day of my life."
This one gives the feel that the speaker wants the death of whomever he is speaking to. The speaker needs it to be happy, needs it to completely his life, whereas...
"If you die tomorrow, I will not shed a single tear."
gives the idea that the speaker simply does not care about the other person. Not that the speaker needs to wants to induce death, but that other person means nothing to the speaker, which renders it less cruel because it's not as concerned, if that makes any sense? The first quote would take a lot of emotional power by the speaker, the second doesn't.
But, you should try to take it one step further. Add even more emotion and add originality.
“It's necessary to have wished for death in order to know how good it is to live.” ― Alexandre Dumas, The Count of Monte Cristo
"I'll prepare for your funeral. Do you think these earrings will look good?"
"I wish you killed yourself when you had the chance."
Ubi caritas est vera, Deus ibi est.
"The mark of your ignorance is the depth of your belief in injustice and tragedy. What the caterpillar calls the end of the world, the Master calls the butterfly." ~ Richard Bach
I am nothing but a mouthful of 'sorry's, half-hearted apologies that roll of my tongue, smoothquick, like 'r's or maybe like pocket candy that's just a bit too sweet.
"If you were to die tomorrow, my greatest regret would be that I didn't kill you."
This is one little planet in one tiny solar system in a galaxy that’s barely out of its diapers. I’m old, Dean. Very old. So I invite you to contemplate how insignificant I find you.
