My top peeve remains "I" for "me". With the recent example of "John and I's new boat", urgent action is needed.
Anne Louise Marquis's recent FB post from an article which used "misnomer" for "misconception" reminds me of this rarer but almost as annoying peeve.
I'm not a professional peever: I don't get hot and bothered about people using "decimate" to mean more than the destruction of 1/10 of something. I am a fan of the singular "they". And I certainly don't go for supporting rules that were made up recently on the basis of nothing more than a whim, like ending sentences with a preposition or splitting infinitives.
So trust me when I peeve!