As a career copy editor, I've had to know a lot about the niceties of language, including the difference between insure and ensure, imply and infer, lie and lay and other pairs of words.
In everyday speech, some non-editors often get these words confused. I think this drives some copy editors crazy. Some grammar sticklers even correct those who misspeak.
Although such distinctions are important and need to be observed, there's no reason to go ballistic if someone, in speech, confuses imply and infer, for example. My mother got these words confused all her life. But she wasn't a writer, and she also played a key role in the successful raising and feeding of six children. And she had more common sense than a lot of folks who have doctorates.
In addition, correcting someone's speech could have its risks, depending on the situation, as I mentioned in this previous post (which for some reason has received a lot of hits, according to Site Meter).
But if you really want to get my goat (and you're welcome to the smelly creature), there's one area, involving not easily confused words but grammar, that can get to me (and my goat; he may be smelly but he does have some sense of literacy).
A local car dealership has an ad that includes the following jingle, which I've changed slightly to remove the name of the dealership (why give those folks a free ad?):
IT WOULD BE A PITY
IF YOU DON'T SHOP AT AUTO CITY
"NO NO NO," I want to say in full-blown Daffy Duck mode, "IT'S 'IT WILL BE A PITY.' OR CHANGE 'DON'T' TO 'DIDN'T'!"
I feel better now. Thanks.