What is Justin Guarini's hair made of? Jheri Curled caramel? (Actually, that must be what he uses to lubricate his vocal cords.) I certainly had a lot of time to contemplate the question when I saw From Justin to Kelly, the appalling bland de soleil musical that's the latest demonstration that reality TV tie-in movies don't work. Just pretend, for a moment, that they did. Imagine that six months from now, your local omniplex is dominated by the 5,000-screen nationwide opening of movies like ''The Real Bangkok and From Clay to Ruben.''
But I digress into nightmare. How bad is ''From Justin to Kelly''? Set in Miami during spring break, it's like ''Grease: The Next Generation'' acted out by the food-court staff at SeaWorld. Justin, cast as the cool-dude ''mayor'' of spring break, spends the entire movie getting his text messages crossed with nice girl Kelly Clarkson. He may, in other words, have missed nabbing the crown on ''American Idol,'' but he's still chasing after the winner. You could say that the beach-blanket imbecility is no worse than what we got in '60s musicals like ''Where the Boys Are,'' except that Connie Francis didn't sing as if she were selling passion by the yard.