"That artist's work literally blew me away."
"I'll go walking in the park irregardless of the weather."
"I could care less what they think about my idea."
Do any of the sentences above seem wrong to you? Perhaps they all sound fine. Certainly they all contain commonly spoken words and phrases. Yet, if you pay close attention to the expressed sentiments, you'll find that all three examples demonstrate verbal misuse.
Literally means exactly or accurately. So unless the artist mentioned in the first example created an excessively strong wind gust, their work could not literally blow me away. But it could do so figuratively—that is, metaphorically—if it was astoundingly beautiful.
AWFUL stands for Americans Who Figuratively Use Literally. According to Steven Pinker's book, The Stuff of Thought, Roger Tobin coined this acronym. The book says:
The charter member was Rabbi Baruch Korff, a defender of Richard Nixon during his Watergate ordeal, who at one point protested, "The American press has literally emasculated President Nixon."
As our language evolves, using literally when speaking figuratively is becoming more accepted in informal speech as a method of exaggeration. However, in formal writing, I recommend you use both words precisely. When you're literally correct, you avoid figuratively pushing proper English out the door.
If you regard the weather, that means you pay attention to it and take it into consideration when making decisions. Add the suffix -less, and you have no regard.
The prefix ir- means not. Thus, irregardless means you do not have no regard—a double negative that literally means you do have regard.
Irregardless may be a combination of irrespective and regardless, and most people understand the implied meaning. However, it is considered substandard English, so it's best to avoid this double negative, regardless of how its misuse is commonly accepted.
The third example suffers from a problem similar to the second. People generally use "I could care less" to mean they don't care at all. Yet they must have some quantity of caring, or there would be no way to lessen it. In this case, the phrase needs the addition of a negative: "I could not care less."
Why It Matters
Why care at all about verbal misuse? Consider what George Orwell wrote in his essay, "Politics and the English Language":
"[The English language] becomes ugly and inaccurate because our thoughts are foolish, but the slovenliness of our language makes it easier for us to have foolish thoughts."
If you couldn't care less, and you want to misuse words and phrases, regardless of the consequences, there's literally nothing I can do to stop you. Just be prepared to figuratively slip into a puddle of sloppy thinking.