I have quite a few:
-I agree that Head On has got to be one of the worst commercials in history.
-Any of the Cialis-esque pill commercials are irritating. Especially the one where the two people are sitting in a bathtub.
Although the Viagra commercial where the guys are all out on the street singing "We Are the Champions" was pretty funny.
-Most of the Red Stripe commercials are stupid, and I'm offended by the one about 'helping our white friends dance."
-This may have been a regional one that was played constantly where I used to live for a place called CashCall (I think). It had two things: Gary Coleman, and the worst jingle ever.