that tears it
1. That's been ruined or spoiled. Well, that tears it for our chances at getting re-elected. A: "That didn't sound good." B: "Yep, that's torn it—the engine is completely shot now."
2. I've had it; that's enough. OK, that tears it, I'm calling the police—it's 2 AM and that party is still blasting music.
tear it
Ruin something, spoil one's chances, as in She knew she'd torn it when she lost the address. It is often put as that tears it, as in He's a whole week late-well, that tears it for the September issue. [Colloquial; early 1900s]