I've never been a MM fan either. The "Happy Birthday Mr. President" moment wasn't sexy, it was a forced, stilted, caricature of sexiness.
Every time I see that clip, I can't believe it ever was allowed to see the light of day, and I remember it being played on television at the time. Poor Marilyn was so impaired she could hardly stand up and get the words out. And her dress was skin tight and translucent if not exactly transparent. Her "performance" was pathetic and embarrassing, yet such was the power of the media idolatry of anything related to the Kennedys, it was presented as if it was a knockout celebrity "event". It gives me the willies when I see it.