To whom it will concern

"I'm going to teach you that having kneecaps is a privilege, not a human right".

Half of these are just OOP's kinks showing

I will moisten your socks

I will grant you immortality then lock you in a box

I used to RP a character in Ultima Online that would threaten people with "I'm going to remove your larynx through your sphincter."

Enjoy your next 24 hours

I’ll clog your toilet

"I will stare into your eyes even after you blink".

"I want to collect your shadow"

It's from the band Craft's song I Want To Commit Murder. Pretty great black metal.

I always thought the idea of biting someone else's tooth out was unsettling.

There's a repeated line in "Once Upon A Time" that is supposed to be romantic, but taken from another point of view is very unsettling.

"I will find you. I will always find you"

"Invert your rib cage"?

Oooold.

https://en.m.wikipedia.org/wiki/Blood_eagle

I'll hit you until I pass out

"I'm about to become the reason your children will have nightmares"

I will salt your papercuts.

I will grate your cheese.

I shall end your bloodline, with a spoon.

When asked what their biggest fear is most people say stuff like "spiders" and "heights"... And I'm always like "why is never anyone thinking about being tortured to death?" is there something worse? I doubt it

Where I'm from, there's the expression "you'd look good in a binbag", which is supposed to mean that you'd even look good wearing a binbag, but I've always thought it sounds like someone wants to chop you up and throw you in the bin.

I did once have someone come at me while saying "I WILL RIP YOUR EYEBROWS OUT"

My personal favorite is:

"I will walk through you"

One of my go-to phrases is "Imma feed you to a cow".

"when I'm finished, you're gonna be in multiple time zones at once."

You will go nicely with the lamp base I just bought.

One I've always wanted to try is "I will keep punching you until I break through your head."

I always liked Digger’s threat to Herne: ‘and furthermore, should you hurt its feelings, I will smelt ore with your bones, understand?’

I will unfuck your mother.

My favorite: Don't make me shove a straw in your carotid to see how far I can make the blood fountain shoot.

"I have a use for you."

"I'll send your teeth brush to the unemployment office" or "Carmine, you sit in the front seat, I wanna stretch my legs", I for myself like to use "you have my undivided attention now", freaks people out. Don't have to use it very often, one or 2 times in my life in earnest. Add Jack Nicholson smile for good measure.

Eh, I wouldn't call those unsettling. Humorously over the top to me.

Something more akin to "I will fucking beat you until you shit yourself" is unsettling. Going with "I will shove a dildo studded with tacks in your ear" is just absurd.