I am such a vocabulary/literacy snob that one reason I really disliked a previous boss was she constantly said "you have to remain cognitive of what's going on." It made me crazy. I bet half of what she wanted me to be cognizant of went in one ear and out the other without stopping because inside my head I was screaming, "remain cognizant! remain cognizant!"
What's your peeve? You know you've got one. Is it a "mute" point? Or "irregardless"? Or "ATM machine?"
And: is there etiquette for letting people know when they're saying something that makes them look bad (like the physician I worked with in the ED who pronounced Cardizem "card-dee-a-zem")?