Untrue things widely believed might be considered "fakelore," such as the folk etymology you post; I'd add three:

-The acronym for "Fornication Under Consent of the King" does not provide our earthy word for the conjugal act. The word's recorded long before that that modern English phrase would've made sense;

-Posh did not stand for "Port Out, Starboard Home;"

-"Tip" did not come from a basket labelled "to insure promptness"

But to qualify as folklore rather than mere errors, I'd think the beliefs have to be factoids that are useful in supporting some worldview:

-"Ring Around the Rosey" has nothing to do with the Black Death (though I recognize there's a number of long threads on the subject, and mine is a partisan position); this is useful for suggesting that children are wiser, more aware and resilient than we give them credit for, or that their games have a deeper historical memory than we might credit (which things I believe to be true; I reject the equation of "myth" and "folklore" with "falsehood");

-There never was any such thing as a "droit du seigneur" or "ius primae noctis"; there may be a hint of such a thing in Gilgamesh (5000 years old); the democratic myth was fostered by Voltaire and Mark Twain;

-Einstein did not flunk math, but the story reminds us that institutions do not always deal well with the gifted.

Richard Dorson, who coined the term "fakelore," meant something a little different, and I don't mention this to be picky or pedantic, but it might make a worthwhile subject of conversation in itself. Fakelore occurs when anonymous mass-culture enterprises co-opt folk materials and sell them back to people, or invent "traditions" out of whole cloth (Paul Bunyan). Some country music surely fits this, though we'd want to be careful to acknowledge that living traditions are dynamic, and should be expected to exhibit growth, change and adaptation. And sometimes, commercially-generated stuff can enter the folk, and begin to be transmitted and adapted outside of these commercial and institutional contexts (Montgomery Ward's "Rudolf the Red-Nosed Reindeer" for example).

Best,

Adam