It's a general expression for you killing somebody. You've heard of this. You've seen this, right? You know what that is. Everyone knows.
9 seconds sound clip from the Guardians of the Galaxy (2014) movie soundboard.
You can hear this line at 00:30:40 in the Blu-ray version of the movie.
Quote context
[...]
- She betrayed Ronan. He's coming back for her.
- And when he does, that's when you...
- Why would I put my finger on his throat?
- What? Oh, no, it's a symbol. This is a symbol for you slicing his throat.
- I would not slice his throat. I would cut his head clean off.
- No, no.
- What I'm saying is, you want to keep her alive. Don't do his work for him.
- I like your knife. I'm keeping it.
- Listen! I could care less whether you live or whether you die.
[...]