I suppose it's poetic justice.
3 seconds sound clip from the Back to the Future Part II movie soundboard.
You can hear this line at 01:00:39.478 in the Blu-ray version of the movie.
Quote context
[...]
- Go ahead, kid. Jump. A suicide will be nice and neat.
- What about the police, Biff? They're gonna match up the bullet with that gun.
- Besides, they couldn't match up the bullet that killed your old man.
- I suppose it's poetic justice.
- Two McFlys with the same gun.
- Idiot.
- You're not gonna believe this.
[...]