The English language is under assault by stupid people who use words they don't understand, and is defended by pompous asses who like to correct those people. We're not sure who to side with.
So, here are some words that you'll see used incorrectly on a daily basis, and a helpful guide as to just how big of a dick you'd have to be to correct people on it.
People think it means: Regardless.
Actually means: Not a damned thing.
This is not a word. Now, we have no problem with making up words (if a particular scent can only be described as "fartalicious," we reserve the right to call it so). The problem with this one is "regardless" already means something isn't worth regard (that's why the "less" is there) so adding the "ir" to it means... it's worth regarding again? Who knows.
People think it means: To skim over or browse something.
Actually means: Almost the opposite of that.
Peruse means "to read with thoroughness or care." If you peruse a book, you leave no page unturned. This makes sense when you consider the Middle English per use, meaning "to wear out or use up." Unfortunately, if you "consider the Middle English" very often when speaking, you're probably not exactly the life of the party.
People think it means: Any kind of amusing coincidence.
Actually means: An outcome that is the opposite of what you'd expect.
So, if a porn star moved to Virgin, Utah, that would be ironic. If the same porn star bought a house in Boner Knob, Montana that would not be ironic.
People think it means: "Spotless" or "as good as new."
Actually means: "Ancient, primeval; in a state virtually unchanged from the original."
It's therefore perfectly possible to have a pristine mountain of fossilized brontosaurus shit, but if you were to buff that mountain to a lustrous shine, it would no longer be pristine.
People think it means: Unperturbed, not worried.
Actually means: Utterly perplexed or confused. It comes from the Latin non plus (a state in which nothing more can be done).
The misunderstanding would seem to stem from people making semi-educated guesses as to the word's meaning, which kind of sounds like it means "unruffled" or something like that.
People think it means: Mildly amused.
Actually means: Bewildered or confused.
If you were to say "I was bemused by your dead baby joke," you wouldn't be saying the joke was funny. You'd be saying that you completely failed to understand it. You were following the story up to and including the bit about the trowel, but you'd lost the thread way before the Ku Klux masturbation climax.
People think it means: Enormous.
Actually means: Outrageous or heinous on a grand scale.
War crimes are enormities. Extra-big bouncy castles are not.
People think it means: A lot of something.
Actually means: Too much of something, an over-abundance.
It's the difference between: "Dude, I am jonesing to go snort a plethora of medicinal-grade barbiturates right now." And ... "Dude, I just snorted a plethora of medicinal-grade barbiturates, and now there are hundreds of terrifying arachnids crawling out of my penis. They all have human lips."
People think it means: Nobody is sure.
Actually means: Nobody is sure.
Specifically, we're talking about when the word is used with some other adjective. Like if somebody says, "The turd pool is deceptively shallow," does that mean it's deeper than it appears, or not as deep?
If you're not sure, don't feel bad. The American Heritage Dictionary asked their word experts and they said they had no fucking idea, either. So ... nobody knows.