The Bee Gees – "Night Fever" and "More Than A Woman" from the Saturday Night Fever soundtrack were darn decent. But God, also "Tragedy" and a bunch of tunes with Barbara Streisand. Gak.
Genesis – This band started out well ("Turn It On", most anything from Abacab, etc.), similar to Chicago, above. Eventually, though, they splintered off into Phil Collins/Mike and The Mechanics and made music that wanted you want to kill yourself, and others.
Feel free to post your embarassments as well.