Groups of people who deliberately take up the whole sidewalk/hallway and walk REALLY SLOWLY. Same for people who hang out in groups chatting in front of doorways. Really people, you can't talk anywhere else but the spot where you get in everyone's way?
Also people who design gender based ads. Either of the "Guys are all bumbling idiots" variety, of which there are DOZENS and all of them are insulting, or the "ITS FOR DUDES, NOT CHICKZ" variety (I'm looking at you, Dr. Pepper 10). It's only okay if it's meant to be funny, like the Old Spice guy ads were.