This first date is going terribly.
The movie is full of this. Tina, Nancy's best friend and the movie's obligatory "You ain't cool unless you're MAKING OUT!" character, wakes up with a tattered night gown after dreaming about Freddy Krueger chasing her. Soon, all of the teens realize they've all been dreaming about Freddy Krueger, our little puberty Sandman. And as with puberty, no one is initially equipped to deal with him in the slightest.
As the movie progresses, the looming presence of sex starts to dominate how Freddy menaces the teens. While Nancy is sleeping, we see Freddy appear over her bed, the wall resembling a rubbery condom that a nasty little demon head is trying to poke through.
New Line Cinema
The viewer is even present for a scene representative of Nancy's first period. As Nancy lays in the bathtub asleep, Freddy's clawed glove breaks through the surface of the water between her open legs. This isn't just one of the most intense scenes in horror history. It's clear foreshadowing of all the trouble that's about to happen between your legs. From periods to wet dreams, they're the first milestones that will take the allegorical teenager down a snowballing Domino Rally of confusion and destruction that'll last anywhere from 10-70 years.