To all intense and purposes.
Pedal to the medal.
I could care less.
These are somewhat of a pet peeve of mine, I don’t mind if you use cliches, but I do mind if you use them and get them wrong, and then insist that you aren’t wrong, and even when shown a definitive source will still insist that you are right and that the OED and all other sources are wrong.
I can understand how it is possible for someone to get these and many others wrong, after all most people do not sound out each and every syllable of a word in a sentence and when you speak quicky ‘to all intents and purposes’ sounds very much like ‘to all intense and purposes’, however when you write it down it should be very obvious that intense in that sentence does not make sense or fit in with the rest of it.
The same with ‘pedal to the metal’ spoken quickly it can sound like ‘pedal to the medal’ however once you write it down the same thing applies, knowing that it means to ‘put your foot down’‘ or to just hurry up at full speed, then medal just does not fit or make sense.
And using ‘could care less’ instead of the obvious ‘couldn’t care less’ is just sheer laziness, just analysing the saying should show you why you are making a mistake, obviously if you could care less then you do care at least somewhat.
I could write whole pages on sayings that people mangle, most are just due to mishearing things, when you say them the glaring error isn’t quite so obvious, but when you write them down, and insist that you know better than the whole combined intellectual might of the OED, then I will call you on them.