The pre-chorus vocal melody to Taylor Swift's Bad Blood (released May 17, 2015), which features Kendrick Lamar, echoes the chorus vocal melody to Iggy Azalea's Fancy (released February 17, 2014), which features Charli XCX. Compare the lines, Bad Blood: "It's so sad to think about the good times," with Fancy: "I'm so fancy, you already know. In addition, the bridge vocal melody to Bad Blood (2:40), starting with the line "band-aids don't fix bullet holes" is reminiscent of Swift's own We Are Never Ever Getting Back Together (:54) and the lines "You go talk to your friends, talk to my friends, talk to me."
The chorus to Britney Spears and Iggy Azalea's Pretty Girls is reminiscent of the chorus to Nu Shooz 80's hit I Can't Wait (released February 1986), in terms of production/arrangement (synth sounds, bass line, claps/snaps on two and four, and tempo). In addition, the double-tracked (or Antares' effected) lead vocal is similar to Gwen Stefani's lead vocal sound in Hollaback Girl
The synth bass hook to Iggy Azalea's Fancy (released February 17, 2014) is similar to the wah-wah guitar hook to the Grateful Dead's Shakedown Street, from the band's album of the same name (released November 15, 1978). Fancy's riff is in the key of C minor and has the pattern b3-2-1-5-5-b3-2-1, while Shakedown Street's riff is a whole-step higher, in the key of D minor, and has the pattern b3-2-1-b3-b3-2-2-1. [Thanks to Andrew Zucker for suggesting this one!]