Need help figuring out a character's dirty secret

[ArthurAleksei]

I'm in the development stage of a slice-of-life/drama type story that takes place in a modern-day town. In one part of the story there's this girl (we'll call her Nasty for now) who's bullying a younger/smaller/weaker schoolmate. She's sort-of popular/"cool"--but not top-of-the-foodchain or anything.
My idea was that this other girl, who's a delinquent that's into goth culture (we'll call her Goth), decides to dish out some vigilante justice. My idea is that she spray paints a message on Nasty's locker. Basically a phrase or word that suggests she knows some dirty secret of Nasty--blackmailing her to stop bullying the other kid.

The problem is, I have no idea what the secret is, so I've finally decided to see if anyone here might have an idea. It could be anything really, except for murder or any other kind of felony (I'm not writing a mystery thriller here!). It could be something that ruins her reputation, gets her kicked out of school...

EDIT (extra character details):
To be honest, i don't have very much character development on the bully character done. She's actually a bit more of a plot device right now!
I imagine she does have her own clique, so maybe her fear has something to do with how the others in he clique would respond to this secret--although maybe her inner circle of friends are actually in on it too (they might be guilty too?), and she's more scared of others finding out. She might have a bit of a goody-two-shoes quality to her, but I'm not sure.

The kid she's bullying is from a poor family. I'm thinking that his father is in prison, and his mother is a recovering drug addict, but this is likely going to be hinted in the story rather than explicitly told.

Both characters are actually just side characters, as this sub-plot is more about the goth-girl character. Goth is by far the most developed character of the three (since she'l be in the main cast). She's a rebellious girl who doesn't really care about how others perceive her, but she's actually quite smart and attentive. She's able to see things about people that others miss. And as showcased in the scene I mentioned, she has a bit of a vigilante streak to her.

[AnimeKitty]

I would really need to know more about the characters to get a sense of a secret they'd have. As a mystery/thriller writer, my first ideas jump to murder and felonies... But I'll ignore those ideas. Maybe she pretends to be really smart in school but is actually only getting by because she cheats? Maybe she pretends to be more wealthy but actually isn't, so she steals nice clothes and stuff to keep the ruse up?

[ArthurAleksei]

I would really need to know more about the characters to get a sense of a secret they'd have. As a mystery/thriller writer, my first ideas jump to murder and felonies... But I'll ignore those ideas. Maybe she pretends to be really smart in school but is actually only getting by because she cheats? Maybe she pretends to be more wealthy but actually isn't, so she steals nice clothes and stuff to keep the ruse up?

That's an interesting idea. not sure if it'll work, but I'll give it some more thought.
I'll edit in some more details of the characters into the original post

[DokiDokiTsuna]

It could be something that ruins her reputation, gets her kicked out of school...

My first thought was to imply that she's taking drugs. ^^; Or selling them...that would be pretty devastating if Nasty was a sort of 'preppy'-type popular girl whose reputation hinges on her being seen as perfect and pure.

What else...the key is to attack her insecurities, I think. So if she's big on physical beauty, imply that she's had plastic surgery, or that she dyes her hair, or that she uses makeup to cover up some sort of skin blemish, or maybe she pads her bra (teen stuff, idk). ^^

Or if her pedigree is important to her, imply that she's adopted. Or if her grades/sports achievements are important to her, imply that she uses bribery or her own blackmail to get school officials to falsify her records. Stuff like that.

I don't know how you would condense those into threatening phrases, though...that depends more on how you write the issue into the story, how much Goth actually knows, and how many people the message is meant for: is it supposed to be something everyone can understand (and shame Nasty for before the full secret is even revealed), or a secret sort of code phrase that only Nasty will know the meaning of...?

[ArthurAleksei]

I don't know how you would condense those into threatening phrases, though...that depends more on how you write the issue into the story, how much Goth actually knows, and how many people the message is meant for: is it supposed to be something everyone can understand (and shame Nasty for before the full secret is even revealed), or a secret sort of code phrase that only Nasty will know the meaning of...?

It's mainly meant for Nasty, but if it starts some rumors that's fine too.
As for what the phrase/word will be, I'm not too worried about, since i think it'll be easier to figure out once I have the secret down.

[crimson_mystery_cake]

Her secret is that she doesn’t know how to read and she’s mad because she can’t read what goth wrote on her locker.

[coppermouflon]

Ok, read all the other replies and with what you have said, there are plenty of ideas here. Anything beyond that would require developing all the participating characters further.

I like what @DokiDokiTsuna has said, for everything that matters to Nasty, there can easily be a secret behind it that will hurt her. In fact, it would make sense that what matters the most to her (Nasty) is what she is lacking, and why she is putting such an emphasis on it.
Extra points, if what she is making fun of (that this schoolmate has) is actually her biggest fear as well, as it is her reality that she has not shared with anyone.
Double-Extra points if this issue also bothers Goth girl, or can be related to her in some way, so it forces a confrontation and realization/acceptance of her own situation at some point in the story down the road. That way this isn't just a small subplot, it actually also matters to your story.

See what I mean about further character development? I have to start building each character to make this work with whatever I come up with.

So here's an idea that instantly popped in my head, and it built off what @DokiDokiTsuna suggested.
I really liked Nasty being adopted as an idea for some reason. And what the Goth girl spay paints on her locker is the last name (or first name even) of her real mother. This would probably mean nothing to everyone else in the school, but everything to Nasty. (Of course, all this assumes that Nasty is aware she is adopted, knows who her real mother is and is trying to hide it.)

I could go on all day about this or other scenarios, but yeah, it means I build the characters as I want to so they can fit the story, but that wouldn't be right. These are your characters, and your story.

I hope this helps you.

[thirdly]

In my teens I had a bestie that would see more than one guy at once and I had to cover for her. Girls also generally turn on one another when it's revealed that they've been hooking up with their boyfriends behind their backs. When it comes to teens, it's all about dating drama. Makes or breaks friendships. Teens also struggle with their gender preferences...

[fleurravenbooks]

• maybe they are getting good grades by having relationship with their teacher (as gross as it sounds, it happens quite a lot)
• maybe they are lying about their parents
• maybe mother used to be with people in order to get drugs , and Goth found out somehow found out ( you know, like Nasty is mocking someone for the same thing they are experiencing )

[ArthurAleksei]

So here's an idea that instantly popped in my head, and it built off what @DokiDokiTsuna suggested.I really liked Nasty being adopted as an idea for some reason. And what the Goth girl spay paints on her locker is the last name (or first name even) of her real mother. This would probably mean nothing to everyone else in the school, but everything to Nasty. (Of course, all this assumes that Nasty is aware she is adopted, knows who her real mother is and is trying to hide it.)

This is actually a really interesting idea.

See what I mean about further character development? I have to start building each character to make this work with whatever I come up with.

That's true, but I was just at such a complete loss for the longest time that I finally decided to ask for suggestions. As you said @DokiDokiTsuna took a really good approach.
To be honest, with this story in particular, everything always seem to go back to character development.

Some more solid suggestions from @thirdly and @fleurravenbooks.
You guys have given me alot to work with. Thank you!

[ReneVergence]

It may not be a crime, but what if she's a teen mom? I could see that harming the reputation of a haughty, preppy girl if she was trying to keep it hushed up. It could also contribute to developing her more later on it that's a path you decide to go down (whether for better or worse).

[fleurravenbooks]

always happy to help