Pizza / Pasta Hut and Oatibix: Both effectively the same ad, both sound like they've been written by the marketing director's 12-year old son.
Lindsey makes a interesting point about irritating ads in other media. Press and poster ads you can just blank out in a nanosecond, so it's hard for them to be irritating. I get most irritated when ads waste my time, or spoil my enjoyment of something. 95% of radio ads are utterly dreadful, and they get in the way of listening to music, which is irritating. Online ads can be irritating if they pop up in the middle of your screen, but otherwise they are simply 'ignorable'.