I would say that you should go with the first given scenario, your character at a party and the cops show up. It seems easy and might be on of the more fun ones to write (in my opinion)
I will allow you to choose the names for characters, but lets start with the main character, who I'll say is Character 1. Character 1 is a nervous, socially anxious teen who is kind of a nerd. But one of their friends invites them to this party that many people will attend.
You can start the beginning of your story explaining how they got to the party (their friend inviting them and Character 1 is reluctant to go, but decides that they will). Them being nervous about going shows their personality, so be sure to write moments of them worrying about specifics of the party, such as talking to people, or if others will make fun of them because they don't fit in.
About paragraph 2 they would arrive at the party and be intimidated at the amount of teens that are crammed in one big house. Character 1 anxiously walks through the sea of people, praying to find their one friend that they know. Make sure that along the way you are describing the thoughts and feelings of Character 1, and how it affects their actions of course. Character 1 finally meets their friend, and maybe tells them that they feel a little worried about how crazy everyone else is acting at this party. Throwing things around, couples publicly making out, all the things that would normally happen at a party of teens who might be drinking yknow.
Anyway, at paragraph 3 or so is when you could probably introduce the FOIL. Character 2. They would be the one that is throwing this party. Character 2 is a rich, popular, athletic teen who everyone loves, but he can also be kind of arrogant and a bully. Maybe Character 1 spots Character 2 at the party and thinks like, "Oh god, that's [Character 2]. They're the most popular kid in school" and then go on to compare the differences between your protagonist and the FOIL.
The rest of this story should be when Character 2 calls everyone together at the peak of the party to like, encourage everyone to do something crazy (???) You might have to make up the rest on your own, but maybe like Character 2 goes like "lets all go outside and trash the neighbors house" which Character 1 will obviously object. Maybe Character 1 can say it out loud that it's a bad idea, and Character 2 makes fun of Character 1. Because everyone at the party follows Character 2 due to them being very popular, everyone also makes fun of the main character.
So everyone goes out and causes trouble. Paragraphs 4-5 are about the cops being called and coming to the party. Try to imagine what the protagonist and the FOIL would do. Remember each of their character traits. For example, Character 1 might get really scared and hide in like the bathroom. Character 2 might be the one to apprehend the cops head on and be like, "I'm not afraid of authority!!" And then they'd throw a bottle on the ground and yell "RUN!!" and everyone at the party just runs in every direction. Out the windows and everything. But I'm getting ahead of myself :)
I think that's all I'll give for ya, of course use this outline to just make your own story and add all the details in between. Hope this helped a bit! And feel free to ask if you need anymore help.
