About 90% of my friends on FaceBook appear to have no grasp on the correct use of the words "to" and "too", and they're damn lucky I don't tell them so!
... and breathe!
The one that's driving me up the wall at the moment is the use of nouns as verbs. The BBC seems very fond of "tasked" at the moment
That is an irritating one! Management speak is full of that kind of carp! Mispronunciation is another thing that annoys me. Fair enough if it's because of you're accent, but there is no need to add letters in to words! For example, my flat mate insists on pronouncing Centaur "Sen-a-tore" (and yes, it does show what a geek I am that Centaur is used enough in my flat for it's pronunciation to become an annoyance to me! )