Here's an example off the top of my head that lots of LGBTQ people repeat and believe firmly to be true: The slur faggot arose as a reference to the bundles of wood (faggot literally means stick, or at least it used to) that church authorities used to build bonfires to execute gay people in the Middle Ages.

I first started hearing that etymology in the early 1980s. People wrote about it in serious articles, talked about it as if it were just obviously true, etc.

But like most folk etymology, it isn't true, and the actual story is even more interesting.

The slur did not begin to exist until the 18th century in the northeastern United States or what would become the United States. By then, some people were using the word faggot to refer to brooms, in reference to the bundles of twigs that were often used to make them.

Etymologists have managed to track down usage in New England where faggot started being used not just for the traditional woman's work of sweeping floors, but to refer to women's work and sometimes to women in general.

By the end of the 18th century, some people in New England had begun to call men who did women's work, or who acted like women, faggots.

Then within a few decades, the other meanings of the word faded out of use. The only remaining meaning was the slur, which by the end of the 19th century had become common in New England and then spread to common usage across the United States by the mid 20th century.

The association of faggot with homosexuality, of course, stemmed from not valuing men who violated gender and sexuality roles. That's very interesting, and to my mind more interesting than the common but wrong belief about how the slur originated.

P.S. Just to make things more complicated, the New England usage may have been reinforced by the "fagging" system in elite British boarding schools where younger boys did housekeeping chores for senior boys. Doing the chores was called "fagging," as a reference to women's work.

However, fag and faggot did not evolve as slurs against gay people in England or Scotland where the fagging custom existed through the late 20th century and where it survives in some forms even today. So the association with the American slur is tenuous.

P.P.S. The word faggot for stick evolved from a Latin word referring to the bundles of sticks that Roman magistrates carried as symbols of their power and authority. Our words fascist and fascism derive from that Roman usage.

How interesting that faggot as a slur derives from the same word fascist came from.