RADIO RIP TIDE: Just how hot is Jazzy Jeff & the Fresh Prince's smash single, "Parents Just Don't Understand?" If there's one true barometer of pop teen appeal, it's Hollywood Hamilton's "Top Eight at 8:00," the KIIS-FM's deejay's weeknightly ranking of call-in favorites. Talk about a sweep. "Parents" has completely demolished its competition, finishing either No. 1 or No. 2 every night this month. Finishing a distant second, with a pair of No. 1 rankings, is Brenda K. Starr's "I Still Believe," following by a pair of regular No. 2 contenders, "Fat" by Weird Al Yankovic and "Yo Twist" by the Fat Boys. . . . One local rock outlet that's not hot is KMPC-FM. Despite its long-overdue format of new, new music, the station has been languishing in the ratings cellar, waiting for a signal power boost and a heavy-duty promotional campaign. The first key exec to depart is program director Sam Bellamy, who resigned last week after a nine-month stint in charge. Whether Bellamy fell or was pushed is open to debate. She said: "I was asked to resign because the station management wasn't happy with where we'd gone." General Manager Bill Ward countered: "She offered her resignation and I regretfully accepted it. But we're still firmly committed to maintaining the new-music format." Ward added that he's interviewing candidates for the Program Director post--here's our suggestion: Promote music director J.J. Jackson, who deserves a pay raise just for laughing at Guy (Lombardo) Kemp's jokes.