My all time number one most hated commercial is that STUPID black and white Gilette ad where they act like if you shave w/ Gilette you are the greatest thing ever. It starts off saying something like "You know that feeling you get after a perfect shave, it's like you're on top of the world, and can do anything" then acts like shaving will get you anything in your life. Dear lord do I hate that stupid ass commercial.
Beyond that one, a lot of the ones mentioned here. There are some really horrible car dealership ones that are on at school, they are just embarassing.