"Mama Used To Say", by Junior. For a long time, back when songs came on the radio, and went away again, and you never quite managed to catch who or what they were, I thought this was Michael Jackson. (Well, it does contain a liberal usage of that "Oooh" thing.) I was never, at the time, entirely sure whether I liked it. Now I am certain.
(Another, much more recent, song has affected me in a similar way: "In The City", by The Chromatics, has been floating around on my work computer for some time now, and I have listened to it quite a bit, frequently finding myself close to hitting the "delete" button. But all of a sudden, having forked out for the "After Dark" compilation, on which it also appears, it has dawned on me that it's a song I can't live without. I can't explain it. But then, love's like that.)