Assuming we’re sticking with generally accepted artists and not dipping our toes into the Brokencyde pool, I’m going with the end of “Good Times, Bad Times” by Led Zeppelin. It’s the worst. He sounds like a cartoon balloon leaking air.
And taking a step down from accepted, “Cold Hard Bitch” by Jet. Granted I might be failing to separate the vocals from the horror of the song, but something about the way it’s delivered is also particularly infuriating. The manifestation of a focus group’s perception of cool.