It was a flashback to NYC in the 1990s. A sea of hunks wearing backward hats, suits and cutoff shirts took over Washington Square Park on Sunday for the first-ever John F. Kennedy Jr. look-alike contest. As Lenny Kravitz’s 1991 hit “It Ain’t Over ‘Til It’s Over” blasted through speakers, seven — more participants were in the crowd but arrived after the contest started — JFK Jr. wannabes showed off their preppy, laid-back fits, rollerblading skills and impressive heads of hair, to hundreds of