As a nutritionist, one that gets me is "healthy" vs "healthful".
If you have a "healthy diet" you either mean your food was in good health before it became food (cows were free of disease, plants were robust, etc) or you tend to eat a lot more then the average person.
Most people actually mean they have, or they want to have a "healthful diet", which is a diet that promotes good health in themselves.
Another that bothers me a ton is "and I," so very many people smugly misuse these words! Sometimes "and me" is actually the correct phrasing! Correcting someone "don't you mean 'and I'?" just makes you sound like a fool when you are wrong!
Mary gave the concert tickets to Chris and me.
Chris and I will attend the concert.
(The trick is, drop the other person - would you say "me" or would you say "I"? It doesn't change when you add another person: Mary gave the concert tickets to me./I will attend the concert.)