Janelle Monae - Make the Bus. Maybe without the guy from Of Montreal singing this would be tolerable, but it's not.
Joni Mitchell - Twisted. I suppose this might be fun on its own, but putting it last on Court And Spark kind of ruins the album as a whole.
Todd Rundgren - Golden Goose. You could make a case for at least one song from most of his albums, but since this Healing is my favorite of his I'll say this.
Roxy Music - The Bogus Man. Yeah, I know some of you love this but there's no accounting for taste. If this were three minutes long it'd still be too long.
Taylor Swift - Bad Blood. Since you mentioned her! 1989 is pretty good but this song sucks, and was a single for some reason. Since you also mentioned Panic at the Disco!, one could make a good case for "Me" by Swift featuring the dude from Panic.
Kylie Minogue - All I See. Minogue's never been the best singer but she's fine when she's in her wheelhouse. This is not.
Rilo Kiley - The Moneymaker. Like the above two, another inexplicable "this was a single?" track. This one was the lead single, too.
Richard and Linda Thompson - The Little Beggar Girl. Like "Twisted", not inherently awful but doesn't really fit at all.
The Shangri-Las - Maybe. There's something tragic about being in a band with your sibling, who's an all-time great singer, and kind of sucking but still getting to trot out the occasional lead vocal. See also Dave Davies and Ani Saunders from the Pipettes.
ABBA - The Way Old Friends Do. Why?
Jefferson Airplane - 3/5 of a Mile in 10 Seconds/Plastic Fantastic Lover. I never listen to this mostly great album in full and these two songs are the reason why. Not sure which is worse and don't feel like revisiting in order to determine that.
The Who - Fiddle About. I know this is short but it's really annoying.
Belle and Sebastian - Me And the Major. Another case where a generally good vocalist is not the right vocalist for the song. They should sold this to Pulp or someone.