(from most to least annoying)

• "Could care less"
• "Seen." incorrectly using the past perfect tense of "see" -- without the word "have" -- instead of using the simple past tense. ("I seen him yesterday")
• "literally" instead of "virtually" or "figuratively," or as an intensifier for statements that themselves are metaphorical or figurative.
• mixing up To/Too/Two
• improper use of double negatives ("I don't need no help")
• anyways, anywheres, everywheres, nowheres, and somewheres
• using "good" instead of "well" ("I write good")
• definately
• using an apostrophe to pluralize a word that ends in a vowel (tomato's, potato's, et cetera)
• "eck-setera"
• "eck-scape"
• "eck-specially"
• "axe" instead of "ask"
• "could of" and "would of"
• mixing up You're/Your
• mixing up They're/There/Their
• the use -- and often massive overuse -- of ellipsis as a pause. Its use is to denote the fact that something has been omitted from a quotation
• "heighth" instead of "height"
• "alls" (it usually only appears as the first word in a sentence)
• "cumf-ter-bull"
• not using "whom" when applicable. (I always -- very quietly -- make an M sound)
• mixing up "then" and "than"
• expresso (I work in a coffee shop)
• whip cream
• the use of "enormity" instead of enormousness.
• affect vs. effect
• The word "forte" -- as in something an individual is especially good at -- is pronounced "fort," not "for-tay." The most annoying aspect of this one is not the mistake itself but the fact that I have literally NEVER heard it used correctly.
• "Where are you at?" (and unnecessary and/or sentence-ending prepositions in general)
• Irregardless
• jewlery ("jew-luh-ree") instead of jewelry ("jew-uhl-ree"). "Jewlry" -- with only two syllables -- is acceptable, I suppose.
• It's vs Its -- using an apostrophe when "it" is possesive pronoun is unnecessary.
• mis-pluralizing terms that have reversed noun-adjective syntax by adding an S to the adjective. ("coup d'états" instead of "coups d'état," "brother-in-laws" instead of "brothers-in-law," "attorney generals" instead of "attorneys general")
• using panini as a singular noun when it it plural. (panino is singular). Also, because I work in a coffee shop, biscotti instead of biscotto.