Any ad which offers a toy when I sign up. Why anybody would choose their car insurance based on whether they get a stuffed meerkat or a toy robot is beyond me, and the implication that I would be swayed in this way is insulting.
Ads which are badly dubbed. If you can't be bothered, or don't think it's worth it, to invest the time and money in an ad which is appropriate to the language and culture of the country in which you're broadcasting it, don't expect me to pay attention.
Ads with children's voices played by adults putting on a phoney child's voice. It sounds annoying and is pointless.
Ads which are considerably louder than the programme during which they are being broadcast. If you make me reach for the remote then you're causing me an inconvenience and I will never buy your product.
Ads which make fun of groups of people such as ads for cleaning products in which the man is clueless about how to clean a house and needs the woman to show him how to use this great new easy product. The implication that poor stupid dirty knuckle dragging man needs clever homely obedient woman to understand the basic concept of cleanliness is offensive to pretty much everyone.
Ads for perfume or aftershave which have no discernible message other than "use this aftershave and you'll become a buff sailor and women will be attracted to you" or "use this perfume and you'll become a beautiful woman and men will be attracted to you"