My nephew is one of my prime sources for Gen Z/Alpha slang, and he just loves the Goomba fallacy.
The Goomba fallacy is a reasoning mistake. When there are two contradicting opinions in one internet community, some readers think that everyone in the community is stupid, because the opinions are contradictory. They do not realise that there are separate people posting in the community, with separate opinions and beliefs. In other words, two groups with contradictory views are perceived as one group that contradicts itself.
The Goomba fallacy was named after the following meme:

What’s a Goomba?
A Goomba is a brown mushroom with an underbite that is part of the Nintendo’s Super Mario franchise. They are weak little enemies that Mario defeats by stomping on them.
(It is also a slur for Italian Americans, which is why the Mario people chose the name. The fallacy has nothing to do with the slur.)
Since when has it been called the Goomba fallacy?
The oldest post I can find on the generally searchable Internet is this Reddit post from 22 May 2024. In the post, people discuss the term as already existing, which I assume would be on non-searchable forums like Discord. My nephew first encountered it on Discord in December 2024.
How do you know the fallacy was named after the meme, and it wasn’t the other way around?
I may be wrong. But the picture above went viral in March 2024. In other words, it seems the picture came first, and the fallacy was named after the Goombas in the picture, which were, presumably, chosen because they had just the right stupid/ignorant/distrusting look.
I have not been able to find any evidence for the word existing before the meme. It’s not impossible, but the above theory seems more likely, also because I cannot think of another reason why it would be called the Goomba fallacy (people who play Mario, please help me here – is there something inherent about Goombas that makes the name ‘Goomba fallacy’ make sense?)
I bet real philosophers have a real name for this
They do. The Goombah fallacy is a specific example of the association fallacy, which asserts that properties of one thing must also be properties of another thing if both things belong to the same group. For example, a fallacious arguer may claim that “bears are animals, and bears are dangerous; therefore your dog, which is also an animal, must be dangerous.” (Wikipedia)
Any other names?
A user on Reddit suggested calling it the Muhammad Wang Fallacy, which I thought was really clever, but it is not a widely recognised name. The idea is that since Muhammad is the most common first name in the world and Wang is the most common last name, the most common full name must therefore be Muhammad Wang.
“Maybe we should just call that “the Muhammad Wang fallacy”: the notion that because a forum includes people who loudly advocate position P and people who loudly advocate position Q, that there must exist a consensus that P and Q is true.
It certainly crops up a lot. Here’s an example from Slashdot some years ago: “You people all hate the movie industry but love Star Wars; how can you be so hypocritical?” One may observe that the forum includes people loudly decrying the MPAA, and people loudly praising Star Wars; the fallacious reasoning is to conclude that they must be the same people — or that the forum as a whole has an opinion.”
(Thanks to u/segwaysegue on Reddit)

Heddwen Newton is an English teacher and translator. She is fascinated by contemporary English and the way English changes. Her newsletter is English in Progress. More than 2300 subscribers and growing every day!
There’s actually a silly reason for the image using goombas. The original version of the meme used “wojaks”, a different type of images used to represent people that has garnered a lot of distaste due to its overuse, particularly in certain very bigoted internet communities.
Someone joked that we should make goomba versions of wojak memes, and this is the one that got biggest, replacing the original.
Here’s a link to someone sharing the original https://x.com/BruhKonata1/status/1813658219006558482
Also, you are correct, the name is based on the image.
THANK YOU!!!!