My BIGGEST pet peeve is: "I could care less" If you could care less then obviously you care. The correct phrase is "I couldn't care less.
You're and your. (This one is inexcusable. Should be an automatic "back to Middle school or lower" card) Should have and should of. Gay. Misunderestimate.
By far my biggest pet peeve is the incorrect use of "ironically" in sports writing and analysis. Almost every time it's used, the speaker/writer should use coincidentally instead. The two words are not interchangeable.