Sends you a text from your spouse's phone number that an emergency has happened and you need to go to xyz location right now. Someone else is a gun owner and they get a similar text, but their spouse is being held captive and are sent to the same location with a description of you as the kidnapper. Scale this as desired.

Use your imagination!

Again, what part of this couldn't an evil human group already do today? What in this plan requires an AGI for it to be a scary scenario?

Of course if you do it to everyone, total gridlock ensues and nobody gets to the place where they would be killed. If you only do it to a few, maybe there will be a handful of killings before everyone learns not to trust a text ever again.

As an aside, I agree living in a country where people will take their guns around and try to solve things vigilante style instead of calling the police, is a very bad thing in general. In all first-world countries except one, and in almost all developing countries in the world, this is a solved problem.

Scale! Do this to two people, no problem you can get a team of folks to dig through their social media, come up with a plan, execute. Might take a day to get a good crisis cooked up.

An AI might be able to run this attack against the entire planet, all at once.

Try to think like a not-human, and give yourself the capacity of near-infinite scale. What could you do? Human systems are hilariously easy to disrupt and you don't need nukes to make that happen.