I'll try to make this make sense. I have heard of examples of people who take a word and wrongly explain its origin, usually in a way that makes sense; it is perfectly feasible for the word or phrase to have developed that way, but is not based on actually evidence of the word developing and is sometimes shown to have been borrowed from another language, entirely unrelated. This is often done by hobby linguists (not a slur). Is there a term for when this happens and does anyone have any examples?
(pseudoetymology, paraetymology or paretymology), sometimes called folk etymology although this is also a technical term in linguistics, is a popularly held but false belief about the origins of specific words, often originating in "common-sense" assumptions.
Such etymologies often have the feel of urban legends, and can be much more colorful than the typical etymologies found in dictionaries, often involving stories of unusual practices in particular subcultures (e.g. Oxford students from non-noble families being supposedly forced to write sine nobilitate by their name, soon abbreviated to s.nob., hence the word snob).
Many recent examples are "backronyms" (acronyms made up to explain a term), as in "snob", and "posh" for "port outward, starboard homeward"; many other sourced examples are listed in the article on backronyms.
I think you're looking for false etymology, sometimes called folk etymology (although that term also has other meanings).
An example of this is the urban legend that the word picnic came from "pick a n****r."
Somewhat similar to this is a false cognate, where two words seem to share the same etymological origin but actually don't. For example, the words human and man seem like they might come from the same root word, but they don't.