I'm going to go ahead and throw the entire calendar year 1997 into my Hate Pit. From my research, no other year has provided as full a list of utterly unlistenable hits. Take a look:
You can't name me a year that can fuck with '97's awfulness.
1999, with the twin ascendancy of teen-pop and rap metal. As other people have pointed out, '97 had the saving grace of a few unassailable albums (off the top of my head, I'd add I Can Hear The Heart Beating As One). There were good albums in 1999, but nothing great enough to neutralize the despair you felt turning on the radio that year.
A sampling:
LFO - "Summer Girls"
Lou Bega - "Mambo #5"
Britney Spears - "Baby One More Time"
Ricky Martin - "Livin' La Vida Loca"
Limp Bizkit - "Nookie," "Break Stuff"
Christina Aguilera - "Genie In A Bottle" (OK, this one's grown on me a little)
Santana ft. Rob Thomas - "Smooth"
Eiffel 65 - "Blue"
Kid Rock - "Bawitdaba"
Mandy Moore - "Candy"
Creed - "Higher"
Shania Twain - "That Don't Impress Me Much"
Marc Anthony - "I Need To Know"
Blessid Union of Souls - "Hey Leonardo (She Likes Me For Me)"
Orgy - "Blue Monday"
edit: Redunancy, misspellings wiped from existence