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 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.
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 infront 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 comming 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 to 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 Tootsuki , 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 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?