How about when people say "I could care less" when they actually meant to say "I couldn't care less"? I've had the fun of correcting someone voicing this vulgar bit of verbiage before:
Them: "I could care less."
Me: "Ah, so you DO care, at least to some extent. Clearly, by your own admission, there is a degree to which you could care which is less than the level of caring you are currently at."
After I confounded the individual with something along these lines(I don't quite recall the exact words I used, but it was pretty close to the above), he just sort of gave me a blank stare for a moment or so as he attempted to process what I had just said, then walked away without saying anything further.
I get that a lot, actually.
Sometimes, someone's misuse of language can be more entertaining than annoying, especially if it's completely unintentional. A few years back, a guy I used to work with(we'll call him George, since that's his name)was talking with a young guy who was considering going to nursing school. George was trying to offer the kid some encouragement by telling him about how people have abilities that come naturally to them, and how they ought to take advantage of these abilities. The word George was looking to use to describe these traits people are born with was the word "innate". Instead, George told the kid "Some traits you're simply born with. They're inept." - now that's what I call irony.
Yes, as Briscojr stated, I mentioned the dreaded "irregardless" in another thread. As a free gift to all OMFGers, I give to you a term you can apply to these individuals trying to sound smarter than they truly are by using words which do not actually exist:
I like to think of them as...iridiots.
Feel free to use it the next time someone hits you with "Irregardless..." but just remember who you got it from.
Then again...I couldn't care less.