Arrrrrgh!
Occassionally people mix up "its" and "it's" and that's a bit of an irritation. I don't like it, but I know I screw up the same way from time to time, and if it's (it is - Got it right that time, yay!) just a one-off flub it doesn't bug me too much. It's like a typo. Everyone makes an occasional error, it's (Right again, yay!) the repeating error that is a real problem.
Lately, though, I've been driven to distraction by people screwing up apostrophe usage and getting plurals and possessives mixed up, it is as if rather than realize "it's" is "it is" they simply reversed the general rule (for which "it's" is an apparent exception) that plural is "-s" and possessive is "-'s" or, worse, they apply the apostrophe completely randomly, mixing everything up. Backwards usage at least has some, if wrong, logic to it.
The strange thing is that I am seeing this done by fairly articulate people. It's (Hey, got it right again. I expect I'll screw up somewhere in this rant. That is one of the rules about usage rants, it seems.) done by people who can spell, who can form complete sentences, and don't resort to irritating "txtspk" that would let me simply dismiss their text as being from someone too stupid to bother with.
Also, it's not just capitalized abbreviated plurals, like "CD's" for "CDs" which, while they bug me, I've gotten to the point where it's not a huge distraction. What bugs me are things like this:
Have you read any good book's?
Those are Orvans.
Huh? Any good book's what? Any good book's titles? Covers? Reviews? And how many Orvans were there? Was there a convention of folks named Orvan? These are jarring. They are potholes in reading. Everything flows fairly smoothly, then *WHUMP* there goes the suspension. Really, any suspension of disbelief is damaged by needing to do error-correction on the text.