Anything by Gino Vannelli. If you’ve never heard him, consider yourself fortunate. He took pretentiousness and affected vocals to new heights in the 1970’s. Listening to his music can actually make me want to throw a cannoli at my speakers!.
As far as the worst song that was ever a big hit, my vote goes to Having My Baby by Paul Anka.
Some of the other most hated songs on this thread such as Macarena and Achy Breaky Heart suffered more from the resentment caused by their overexposure since those songs played endlessly everywhere you would go
for months on end and it drove people nervous (as Alice Copper said).