You could literally prove yourself wrong by exercising just a little intellectual curiosity. Marxism is, at its core, an economic theory based on the idea that democracy has as much a place in the workplace and economy as it does in our political system. If that’s fascist to you, you’re unserious.
Now, if you’re just unwilling to correct or criticize your own beliefs, and you want to conflate Marxism with Stalinism and Tankies, you’re better off just saying so.
Like another commenter said, the most basic explanation is that it’s the literal opposite of “cringe”.
The more nuanced explanation is that it was a term co-opted from hip-hop, originally used to celebrate pure expressions of individuality, personal style, and/or personal belief. It was quickly appropriated by internet reactionaries to celebrate anti-liberal and anti-left sentiments, often ones that were explicitly unpopular or socially unacceptable. Eventually it kind of entered the mainstream internet culture and was sanitized by ironic re-appropriation to mean “the opposite of cringe, even admirable, but possibly a difficult position to defend for any number of reasons”.