This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Shokugeki no Soma
Megumi's momentary musing of Isshiki's... nightly invitations through the dormitory's tube system. Though it seems he does this to all of the girls, since one of them tells Megumi to ignore him and he'll back off eventually.
Subaru Mimasaka alone is this trope. He's a creepy stalker and can make very disturbing faces. Like this.
Not to mention all the stuff he knows about people, which makes others reasonably very creeped out.
It doesn't help at all that Takumi's impression of Mimasaka is evocative of an Apostle from Berserk.
In Chapter 80 Mimasaka was already inside Soma's room waiting for him, to the horror of the other residents (and Ikumi, who was also visiting), showing that he could freely get anywhere he wants. Doubles as a mini-Moment of Awesome for Soma and his Nerves of Steel for keeping a straight face to this.
From the same chapter, Subaru pretty much threatened the angry girls from Takumi's fanclub by telling them he could have stalked every single one of them if he had more time. They immediately went silent with fear.
In Chapter 86, Mimasaka reveals to have obtained a lot of information on Souma's action plan from Mitsuru's cover story on him. We then see a picture of him hiding underneath the desk of the computer Mitsuru was using, without the latter noticing. See him in the fullness of his stalker's glory◊.
Chapter 73: Hisako Arato of all people brings up this moment. She beheads a living turtle in front of the audience and opens its shell. And she doesn't even flinch at all.
Maybe Played for Laughs, but acute readers would certainly feel a tinge of horror when they see Senzaemon's fundoshi coming off after tasting Megumi's cooking. The parallel to his 'stripping as he recognizes immense talent' is acceptable enough, but shouldn't the people involved choose something less sexual about it?
Though if you remember that Megumi's cooking is all about hospitality and thinking of the person eating the food, Senzaemon's fundoshi coming off carries a different meaning. His clothes and stuff remain the same, allowing him to keep a certain dignity.
Erina's father, Azami Nakiri. Full stop. This man has both Erina and Hisako absolutely terrified, and for good reason. He basically brainwashed Erina through force and fear. If Erina refused to toss away food below perfect, he inflicted pain on her by squeezing her arm. Again. He is abusing and mind rapinghis own daughter in a dark room. There's also the fun little fact that he looks like Hannibal Lecter.
And in chapter 134 he informs Senzaemon that he got signed approval from 6 of the Council of Ten members to become a new general director, which means he now has the power to do what he wants, effectively becoming a central villain of the story. Things are about to get worse, especially because Azami has made it clear by now that he wants Tootsuki to be only about the highest, most refined levels of gourmet cuisine, all while viewing anything else as nothing but garbage, which can only mean bad news to students like Soma and Megumi, as well as some research societies like the Don RS, who specialize more in humble, homey meals.
To make matters worse of the Council of Ten members that signed control over Azami, two of them are Rindo and Tsukasa. Signing it seems like something Eizan would do and we don't know enough about the other three as characters yet. But, until this point, both Tsukasa and Rindo had come off as Reasonable Authority Figures who seemed to genuinely approve of cooks like Soma and Megumi being a part of the Academy. Seeing them support Azami like this is jarring to say the least.
Even scarier is that chapter 136 reveals that Azami IS the reason that Erina is so haughty over the series. His method of 'training' Erina is to take her into a dark room and force her to eat dishes, pointing out their good points and bad points with her God Tongue, and then throw them away if they don't fit their standards. He even goes as far as to twist her arm when she noticed that she shouldn't waste food until she developed her current personality. This is the main reason of why Senzaemon expelled Azami from Totsuki, as he found the training to be brainwashing.
The lingering effects of this abuse on Erina is heartbreaking and horrifying in parts. Erina has a nightmare based one of the few times she tried to stand up to her father about wasting food and he coldly remarks that he has no need for a useless child and she, reverted back to a child, finds herself in the wastebasket he forced her to dump "bad" food into. It seems almost funny, but to anyone who has had difficulties with difficult to please parents or family members, it sums up lingering feelings of worthlessness and abandonment perfectly. Even worse, from her remarks to herself, she's been having this nightmare for years.
Chapters 173 and 206 show that most of the student body worships Central now. Hell, the page for Urara's reintroduction outright states she's brainwashed and even shows her and other students with swirly eyes similar to the ones in Danganronpa 3. This heavily implies that Azami is basically a cult leader at this point.
In the 3rd season's ED, half of his body is demonic.
Chapters 150 and 151 show that Azami greatly admired Jouichiro. While this has been noted as CMOA for Jouichiro in that he was an awesome enough chef that a complete snob like Azami idolized him, it also raises a few more frightening questions. Jouichiro's nickname used to be Asura and Fumio has noted that his learning to cook with kindness is a relatively recent development. In other words, just what kind of person was Jouichiro back in the day that would cause someone like Azami to admire him so much?
In Chapter 196 we get the answer; Jouichiro utterly CRUSHED fifty of Tootsuki's most promising chefs in a series of ten-on-one Shokugekis in the incident that earned him the title "Asura". The smile on Azami's face as he watches makes it clear that this is where his elitist mindset took root.
Chapter 173: The look◊ the examiner has when gloating to Erina about failing Soma's team due to sabotaged ingredients is like something out of a horror manga.
Chapter 196: Saiba's reaction in the past to his skills being brushed off as those of a "genius" instead of being the result of all his own efforts and experiments. The sight of him standing with an emotionless look on his face above his fallen opponents shows why he was nicknamed "Asura". It doesn't help that we see the first true In-Universe hints of just the kind of person Azami is.
Saiba: Despite havng zero inkling of just how difficult it is trailblazing new paths, you dare dismiss me as just a genius. Must be nice to be so carefree, huh? With that half ass resolve, did you really shout at me to "cook seriously"? Huh? If you don't plan on putting out a plate, then just quit already. I'll give you your last rites.
Chapter 209: One thing is made clear. Don't piss off Satoshi, or he will crush you.
Chapter 219: Rindou's Slasher Smile makes her look downright terrifying, not helped at all by the intense look in her eyes and the knife in her hand, giving an impression that seems more fitting to a horror movie villain than a normally playful and friendly teenage chef.
The protein Rindou decides to use in her match? The world's cutest baby alligator. Anyone who's seen Hisako's turtle burger knows what's going to happen to the poor little thing. And while the manga doesn't show the killing blow, we do see Rindou skinning the little gator (showing the reader a full view of the skinned gator and the meat inside) and looking like the world's most gleeful slasher movie villain while doing so. Even Yuki, a game meat specialist and no stranger to killing and butchering animals, is creeped out.
Chapter 222: We get to see the negative effects of Azami's influence on the world outside Totsuki. The Hokkaido Ramen shop owners were his first victims when 10 out of 20 Ramen shops were shut down in Hokkaido alone for rejecting his cooperation. What makes matters worse is, these people began to show some hostility towards any students (baring Megishima because he was viewed as their savior after saving their failing businesses) from the Tootsuki just by looking at their school uniform, as Soma and Megumi found out. This means anything Azami and Central did will ruin Tootsuki's remaining good reputation, and unless Soma and his friends do something about it, Central's atrocities will be unstoppable!
Soma's beating from Megishima's "discipline session" is too intense to watch. How was that happening? Well, Soma outright proclaimed himself that he will save the Ramen industry once he becomes the First Seat and even challenge the big guy in a Ramen cook-off. Megishima ridiculed him at first but accepted Soma's challenge not as a cooking competition, but as the "discipline session" so his kouhai will know his place, and he succeeded. You'd expect given the "lesson" from Megishima should've force Soma to give up, right? Heck no, because Soma wanted to challenge him again until he wins...and the result still the same. Even so, Soma just won't stay down to the point even Megishima himself begged him to give up!
Chapter 227: Despite the best efforts and innovation from Kuga, Megishima and even Subaru that are well-praised by WGO judges, the prowess of Eishi, Rindou and Soumei is proven too much as they win 3-0; what's further adding insult to injury is Eishi rubbing it in Soma's face by apologizing for spoiling his efforts in looking for his allies. Judging by his glare and a clenched fist, Soma is clearly NOT amused after hearing Eishi's mockery. Not. One. Bit. Although, this is somewhat averted because, despite the defeat, it did temporarily wear out the winners to the point they had to recuperate for the entire day (Rindou's case would be more than that).
Chapter 234: The moment where Eizan gains his momentum by using artichoke to counter Takumi's pizza which, by the way, was already in the oven. His horrible faces aren't exactly helping the situation either.
Chapter 236: As awesome as it sounds, it's rather edgy to see Takumi's tactic against Eizan in a way we never expect: He firstly glared (or rather observed) glare at Eizan, who was using artichoke for cooking his dish, while muttering an ominous message about how he got ahead of the Food Alchemist and he was glad that everything is according to plan. In fact, his pose itself looks like Subaru, makes you wonder if he is possessed by the copycat's soul or something...
Chapter 244: Erina's looking a lot like her father in this chapter when she makes her challenge to Momo. Momo's war face on the next page isn't much better