Pufferfish poison can cause zombification

Braindead people not caring about the wellbeing of others or themselves?

Sounds like the individuals you'll find at black Friday sales.

/s but also that's likely the closest you'll get to an actual Zombie invasion.

Zombies are a real thing, Haitians would use toxins on you to trigger your death response making you genuinely convinced you were dead. That signal is so primal that all of your logical reasoning would be completely overridden with a deeply rooted delusion that you are in fact dead. It's kind of like how you can spray ants with their death chemical and they will walk as if they're fatally injured towards the ant graveyard.

EDIT: Here's one of the videos showing this off

Real "life"?

I could imagine a disease turn people delusional and aggressive. What's always seemed unrealistic to me was the premise of zombies being chill around each other and/or animals, but going bonkers when they see an uninfected person.

Also, these people would be done in by cold wheather, injuries, lack of food and water rather quickly, so they likely wouldn't pose the threat they do in movies.

The most likely zombie to exist are from diseases and/or viruses. Zombie deer virus exists which makes deer irrational and fearless but rarely violent, rabies is one of the oldest viruses and still can't be cured once symptoms show and cause violence in animals but not humans, and viruses are always evolving and changing, so the possibility isn't entirely out of the question, but it shouldn't be anything to worry about.

Yes, they are called "republicans".

Yes they are. Capitalism brain-rot has infected most of US workforce today.