Be careful when saying you'll take something to your grave. It might be a short trip.

In a game you could potentially have some sort of Death by Dramatic Irony rule. If a character says something that typically foreshadows their own tragic demise in works of fiction, they get a penalty to defence and saving throws for the next few turns or something. (If nothing else, this is a good way to get players to avoid spouting clichés during combat.)

Transcript

Darth Vader: If you must keep blathering, tell me about my son.
[SFX]: wmmm...
Luke: He was nothing like you.
[SFX]: wmmm...
[SFX]: wmmm...
Luke: To tell you the truth, I didn't even know he was your son.
[SFX]: Whooom!!
[SFX]: Kzzrzzkk!
Darth Vader: You're hiding something from me. I can sense it.
[SFX]: Whooom!!
Luke: I'll take it to my grave.
[SFX]: Whooom!!
[SFX]: Kzzrzzkk!
[SFX]: push... {Luke pushes Vader off a ledge}
[SFX]: fall...
Luke: Or yours. Either is fine.
[SFX]: jump {Luke jumps after Vader}