ALL of those drive me CRAZY...
except the most common abbreviations, such as OMG and LOL - I kind of like those. And I don't mind occasional "kewl" uses, such as "whatcha think" or "I'm gonna" in instances where it is obvious that the writer intends an informal, "cute" style of communication. But I especially hate the random sprinkling of apostrophes throughout a paragraph, or other errors that appear to be accidentally committed by a writer who either doesn't know, or doesn't care about the correct usage / spelling. I REALLY hate it when I make one of those mistakes, and then notice it only AFTER I have sent the email! Thank goodness for our edit button - I have used it more than once on this forum!
But what about the word "definitely"? Most often, I see it spelled as defiantly. But I have seen MUCH more creative spellings than that. I think that sometimes people just give up and type the basic letters, hoping the correct word will be guessed.
I always had trouble with the word "necessary". Before spell check, I pretty much just resorted to "required" to avoid having to repeatedly look it up! But I finally learned it by pronouncing it (to myself!) as "nekasususary". Hey - whatever works, lol!