Anyone got anything else to add to the list?

Half of these are just OOP's kinks showing
- I will edge you then ruin your orgasm
  Like seriously OP just go watch some toe sucking watersports porn on Bing.

I used to RP a character in Ultima Online that would threaten people with "I'm going to remove your larynx through your sphincter."
- Okay, I'll not comment on your comments anymore, I just realized that's extremely silly

Enjoy your next 24 hours
- General well wishes with zero actual threat that come off as extremely threatening

"I want to collect your shadow"
It's from the band Craft's song I Want To Commit Murder. Pretty great black metal.
- Sounds more creepy romantic than threatening, like something a stalker would say.

I always thought the idea of biting someone else's tooth out was unsettling.
- Where have you heard that?! That's new and disturbing imagery to me.
  
  Just my head

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"

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.

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
- Being tortured almost to death is worse, because, once you recover, they can do it all over again
  
  Being tortured to death and brought back multiple times then set free. No amount of therapy will guide you out of the woods after that.
- Uday gonna getcha

One of my go-to phrases is "Imma feed you to a cow".
- this is a great threat, anyone who's watched cows eat, regurgitate, and re-eat, would be horrified.

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?’

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

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.
- "I'mma punch you so hard you're gonna forget tomorrow." heard this once tossed out, he didn't 'win' as other guy had ground game and it was quickly broken up, but it stuck with me. good ol barracks fights. everyone loses.

"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.

"I will eat your babies" stole it from always sunny. Used it once, ended a road rage incident

I will tongue punch your fart box.
- I think there's a lot of people who would reply "don't threaten me with a good time". Dangerous game.
  I am not one of those people, my ass is hairy and no one needs to be exposed to that literal shithole. But I don't judge other folks with freshly nair'd cheeks, y'all do y'all, I do worry about ecoli but they say it's not a problem "¯(ツ)_/¯ "

I will fuck your throat hole
- it just doesn't communicate threat to people that are into it. You toss that out as you're squaring off and someone goes "Oh shit I didn't know this was foreplay-" and starts putting on chap-stick, like, that's gonna wreck your whole plan