The fluoride stare is a subtle, baffled facial expression you automatically show when someone is talking utter bullshit.
You are trying to be polite by not telling them they should go to a therapist, however, while attempting to be expressionless, a bit of your anger and confusion shines through.
This expression is particularly frequent when talking to a conspiracy theorist.
While you are listening to their irrational conspiracy rant, you cannot help but to give them the “fluoride stare”, while trying to avoid gawking at them.
The conspiracy theorist, of course, will either be completely oblivious to your reaction, or will just think you have been brainwashed.
Although you would think the “fluoride stare” would be an insult towards conspiracy theorists, they are the ones that coined the term.
They are so used to receiving this facial expression that they gave it a name.
However, rather than understanding that people give them this look because their opinion is way over-the-top, they believe it is because of the fluoride in the water we drink.
One study shows that fluoride is a neurotoxin.
It is a fact that ingesting great amounts of it is dangerous, but obviously the conspiracy theorists have blown it out of proportion and believe that fluoride is used by the people in power to brainwash the community so that they stay in the dark.
Hence, the “fluoride stare” when you are trying to tell them the “truth”.
The term is increasingly popular in the conspiracy theory community, and started spreading as a tag on Twitter.
In 2016, a now-deleted Reddit user asked “Anybody else been getting the “fluoride stare” a lot lately?” in r/libertarianmeme along with the “fluoride stare” top meme template featuring a bunch of different people giving the particular stare, and the text “when you say something important and all you get back is the fluoride stare”.