Agreed about the howling, bawling double glazing buffoon (bring back mass public hanging, he didn't do it on his own), the first insurance tenner had a certain grotesque genius, the later ones rather less, but my personal pit of total detestation goes to the past Cillit Bang ads. Their ads have improved, sort of, but I have a long memory for such things, and still actively avoid the product.
Then there are the "story" ads like Kenco and BT, but these are very minor annoyances.
My personal favourite ad was the Carling Black Label ad that spoofed most of the K-Tel ads and was almost a feature film in itself.