1. Getting Your Possessives Wrong
They're is something particularly aggravating about people who mix up they're possessives and they're contractions. If you make this error, we hope at least that you take some satisfaction in the knowledge that your driving everyone crazy with it.
2. Mixing Up Your Haves And Ofs
Had you taken a second to think about it, you surely would of realized that there is only one generally acceptable spelling of the word "have."
3. Mixing Up Your Subjects And Objects
Mixing up subject and object in an attempt to sound sophisticated is a good idea for neither you nor I, and whomever does it with regularity should be punished severely.
4. Compound Words That Don't Exist
Alot of people appear to be selectively unaware of the fact that the indefinite article is far too important a word to be mashed together with the nouns it accompanies.
5. Particularly Pernicious Spelling Mistakes
Although this is more a post about grammer then it is about spelling, I wouldn't want to loose the opportunity to point out three of the world's most aggravating orthographical mistakes.
Irregardless of what you may think, the words "regardless" and "irrespective" would almost certainly prefer that you refrain from mashing them together.
Supposably there is a word out there that means "capable of being supposed," but it's slipped my mind for the time being.
8. Killing The Mood
If I was you, I would be more careful about butchering the subjunctive for no good reason.
9. The Dreaded Comma Splice
There is some debate about whether a comma splice is always an error, it can certainly make a sentence sound very odd though.
10. Dangling Your Participles
After considering it for some time, the dangling participle may be one of the most aggravating grammatical errors of all.
Literally means "literally," not "figuratively," and it literally kills me every time I see it misused.
12. And, Last But Not Least ...