I want to talk about some specific words and usage issues that cause trouble for a great many native speakers of English who should know better. Call these pet peeves, if you must. I don't like to think of them as pets, though. Savage beasts all.
Ironic means that the outcome of something had a distinct quality
of unexpectedness to it. But I like to think it means something more.
To me it implies that there are (or were) two possible outcomes or
interpretations of something, one that's expected but turns out to be
wrong, and one that's not expected but actually true. Contrast this with
the word paradoxical, which (to me) implies two outcomes that
seem to be at odds with one another yet are both demonstrably true. Use
paradoxical when there are two true yet seemingly incompatible outcomes.
Ironic is less concrete a word and not as widely understood as
Poignant means keenly distressing to the senses and/or arousing
deep and often somber emotions. It doesn't mean bittersweet. It can be
an outcome of a bittersweet situation, but by itself it does not mean
Decimate means to reduce by one tenth. Never use it to mean "destroy completely." Decimation was (in Roman times) the practice of killing one out of every ten mutineers (or sometimes one in ten prisoners of war), as a means of demoralizing the nine out of ten survivors. The preferred meaning of decimate remains reduction by ten percent. You can use it to mean "reduce significantly," but never use it to mean total eradication.
Irregardless is always incorrect. Use "regardless" unless you want to appear careless or stupid.
Don't say "which" when you mean "that." Example: "The subject which interests me most is philosophy." Use that, not which, in such a sentence. There's a difference between "The crane that was the cause of the accident was demolished" and "The crane, which was the cause of the accident, was demolished." Which should be reserved for clauses set off by commas.
For God's sake learn the difference between it's (a contraction) and its (possessive). The reason people get this mixed up is that the rule for making something possessive, in English, is to add apostrophe-s to the end of whatever it is. So it's natural to think that if you add apostrophe-s to "it," you get a possessive form. Not true, though. The possessive form of it is its.
Learn to use "nor" as the negative form of "or." In particular, don't use "or" in connection with "neither." Don't do: "Using ain't is neither correct or necessary." The word "neither" here demands that you use "nor."
Try not to use "almost always" or "almost never." It's semantically akin to saying "almost infinite." The words always, never, and infinite are absolute and binary. Something is infinite, or it's not. Something either occurs always, or it doesn't. "Almost" and "always" are two different concepts.
Don't say infer when you mean imply.
Bemused has nothing whatsoever to do with amusement. (Read that again.) It has everything to do with bewilderment or befuddlement.
Peruse means to read carefully, not to skim lightly or read haphazardly.
Who versus whom: My advice? Don't worry about "whom" versus "who" unless you're writing for an audience that cares about such things. It's not always better to use "whom" properly. Using it properly can mark you as a self-righteous pedant! It all depends on the audience. My rule is to always use "who" unless you're convinced the reader will object to its improper use. (And you might have noticed, I don't much care about splitting infinives.) Most readers won't care. You're writing for most readers, by the way (and not your high school English teacher), aren't you?
Literally refers to something that actually happened (or is happening) in reality. It represents the concrete reality of something, not anything metaphoric. There's nothing speculative (nor merely descriptive) about a thing that's literal. "He literally went insane" means the person actually became clinically schizophrenic per DSM-IV-TR #295.1–295.3, 295.90. "He literally went ballistic" means the person had enough momentum to follow a ballastic trajectory through space. "He literally melted down" means the person became hot enough to exceed the melting point of his constituent materials. Don't say literally unless you really mean it.