"We built ..." was voted worst song by a few worthy organizations a few years back. For those who grew into liking the hippy dippy stuff that emerged from the psychedelic 1960s and early 1970s, when Jefferson Starstruck made this one, it was viable proof that the "sell out" existed and that Grace Slick not only was crazy, she was a stunt double for the Runaway Bride's eyes (i.e., crazy).
The Cutting Crew did "I just died in your arms tonight" which is in my top 10 worst. There's also "Neutron Dance" by the Pointer Sisters, which sounds like something that's done after the neutron bomb exterminates your music collection (the Pointer Sisters' best song, "Fire," was written by Bruce Springsteen; and he performs it better).
The German band Accept had "Balls to the Wall" which may have been the paramour to luring other metal bands down a road of awfulness. However, that particular room shaker also makes my top 10 (though it's still got a great driving beat). Also in the metal category, Winger's "17" is enough to gross me out as a father (considering Kip Winger was almost 40 when he made the single; PS, he's 5'2" tall). Also, almost anything by Slaughter makes the metal worst list.
Finally, just random notes hitting me as a I type: "Promise" by When in Rome; Fleetwood Mac's "I want to be with you everywhere" (a truly "jumped the shark" tune if there ever was one); and David Lee Roth's "Livin' in Paradise")