Katy Perry (Firework, Roar chorus, almost any song live)
Iggy Azalea (any song, but especially the speaking intro of Work)
Madonna (her voice is what stops me from getting into her, on majority of the songs it's literally unbearable, nasal, thin and whiny)
The Supremes songs (Diana Ross has a very bad voice)
Barbra Streisand (not her voice but the way she sings is so not my cup of tea)
Cher Lloyd (any song)
Beyoncé (I usually love her voice, but there are a few songs (Best Thing I Never Had, Get Me Bodied) where it sounds annoying.
Taylor Swift (speaking bridge in Shake It Off and eeeeyyyeeeeeoooaaaah that follows it)
I love (!!!) Camila's voice on "Suga Mama" 
the way she stresses laaaadddyyy