Please state in which country your phrase tends to be used, what the phrase is, and what it should be.
Example:
In America, recently came across "back-petal", instead of back-pedal.
Also, still hearing "for all intensive purposes" instead of "for all intents and purposes".
Yeah yeah I know. But "set" (fun fact: it's the word with the most meanings in the Oxford English Dictionary) is the transitive form of "sit", so it's more grammatical, more elegant and shorter than "step". Which obviously comes from a mishearing by someone who didn't read books, yet people will still get indignant and claim that it's somehow better! I need to lie down. ;)