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Nightmare Fuel: Glee
The episode "Furt", where we already know that Karofsky is gay and has feelings for Kurt, but the way he stands really close and does a glary/smile thing, along with winking. It looks a little perverse and the audience are left a little violated, along with Kurt.
Brittany's throwaway lines that sound an awful lot like rape, including being visited by aliens.
Santana being outed after some girl overheard her argument with Finn in the hallway—where he tells her to come out the closet—and the girl told her uncle, who is running against Sue for the Congress seat and targeted Santana's lesbianism in a smear ad against Sue. For many a closeted teenager, being outed is bad enough, but for it to happen on TELEVISION in front of millions makes it nightmare fuel.
EVERYTHING about Karofsky's storyline in On My Way. Hey, being outted not bad enough for you? How about your homophobic classmates spamming the Internet with hate-speech about you until you hang yourself? And just in case you could sleep, have Karofsky's dad finding his near-dead body and screaming in anguish. And even while in recovery, his mom thinks he has a mentally ill for being gay and his best friend Azimio cuts contact.
The effects of Bulimia on Marley. She spends her first five episodes looking warm and bright and cheerful, but once Kitty gets in her head and makes her start vomiting all her meals up she gets less energetic, more pale, and more frail. It all comes to a climax during the Gangnam Style performance. the music starts to cut out near the end, the camera is at weird angles, parts of the song speed up or slow down, and at the end Marley is so malnourished that she collapses onstage. The worst part is the insight to the skewed priorities she's developed, and how such a simple line can become really disturbing.
Marley: I'm so hungry. But at least I fit into my dress.
"Shooting Star". A gun goes off at the school. Most of the club is holed up in the choir room, but Brittany is stuck alone in a washroom and Tina is outside the school and can't contact anyone. Marley tries to text her mom, but Millie can't answer because her phone is too far away and she can't risk grabbing it - and Marley starts assuming the worst.
The eerie silence during that scene just makes the whole thing worse. If you weren't spending that entire scene on the edge of your seat, wondering when the shooter would burst through the choir room door, gun in hand, then congratulations, you have Nerves of Steel.
The metronome going the whole time gave the atmosphere a whole new level of scary.
What we learn about Blaine's inner workings in Puppet Master. Let's just say the title is quite apt.