- People who start conversations in medias res about topics of which the hearer has no knowledge, viz: "So I told Harvey that I knew Peter would break his leg if he went there ..."
- People who use discrete when they mean discreet. I've seen it a lot lately.
More here. I especially like: "Using 2 fingers on each hand to indicate 'quote/unquote'."
Also Annoying habits of coworkers.