I too despise the ones that make chidlren want to eat cr*p! things like 'lunchables' and 'cheese strings' which are apparently 'real cheese'!

But the one I CAN'T STAND and have to either turn over or leave the room for, is the Safestyle UK ad: "You know the one: you buy one, you get one free, I say you buy one, you get one free! (all shouted in a northern accent by a viking bloke). Even if we didn't live in a listed building, so could use their windows, I wouldn't touch them with a barge pole!!! AAARRRGGH!

(I'm sure I'll think of more!)