This chapter is dedicated to the best come back, something more popular than UR MUM, and something that always works:
Your Face.
(E.g. "you suck." "Your face sucks."
"What's up with you?" "What's up with your face?")
Side note, please do not use this comeback on someone who doesn't have a face.

She woke up, with her hands tied behind her back, and no memory of how she got there. Come to think of it, she had no memory, at all. what was her name? Did she have friends? Who was she?
  A door opened, and she flinched back from it as far as she could. "Hey, hey, we're not going to hurt you." A man said. He was average height, with brown hair, and brown eyes. He had a nameplate, she needed him to come closer to read.
  "What happened? Where am I?" She had one last question, but she didn't feel safe asking it. She didn't want them to know she didn't remember anything.
  "You got close, Agent S. That's why you can't remember anything. You got close to the Avengers secret base. You're back at HQ now." She could read his nameplate now. Samuel. Sam had called her Agent S? What was that short for? She just wanted to know who she was. Samuel must have seen this, "do you remember anything?" She shook her head. "Your name is Greta, you are our best agent. The Avengers are trying to take over the world, and it's HYDRA's job to make sure they don't. You were on a vacation, when you strolled close to where they hide their weapons." It was all hard to believe. Had Greta's memory been erased, because she was oblivious to the location of these beasts hiding place?
"So I got too close, and they wiped my memory?" Sam nodded solemnly. She still didn't know what the S stood for, but she guessed it was her last name.
"Oh, sorry, the last time you woke up, you were... difficult, as you hadn't remembered anything. I'll untie you." Difficult? She had hurt people. Friends? Family?

She was walked through everything she was supposed to remember; her first and last name, why she didn't remember anything, and what her profession in HYDRA was. "I'm Greta Sora, the Avengers wiped my memory, I was, and still am, HYDRA's spy," Sam had said in front of her for the 5th time. She repeated. "Good. You should be cleared to work on missions soon, but it's only if you want to. No pressure."
"I want to." This was her chance. If she went on a mission, she might get closer to remembering who she was.

She was walked into the cafeteria room. She was always eating on her own, as she'd been told. No one had ever talked to her. She was keeping her head in a book. She grabbed out her notebook. Everything was important. Every. Tiny. Detail.
  I am Greta Sora. My memory was wiped, so I will write everything I learn about myself here:
  I was a spy
  My parents were killed by Ironman
  I had once broken one of Spiderman's webshooters
  I was a bookworm.

She was handed a book, with the title 'Ninth House' by Leigh Bardugo. "You were reading this. You might want to start at the start again though." There was a bookmark, around halfway, in the book. She definitely didn't remember reading that.

She chose to pick up a book about the Avengers. If you can't fight them, use their information against them because you'd never join them. She flipped to the first page, and found the person to blame for the 'Avengers Initiative' Nicolas Fury. She wrote this down. The leader of the Avengers was Steve Rogers, or Captain America. She wrote this down. After flicking through more pages, she found Spiderman. She knew she'd broken one of his Webshooters. He had never revealed his identity. Fun to know.

2 days later- HYDRA facility

There was a knock on her door, and she sat up in her cot. "You're clear to go on missions now." It was Sam.
  "Thanks, Sam. Do you know if there are any missions based around the Avengers?" Greta opened the door to find Samuel leaning next to it.
  "Theres one." He began walking to the 'war room'. It was the mission room, where they kept the missions that needed to be done, but they liked giving things cool names.

She was allowed to go, in 3 days. She had a side mission, before then, but the important thing was that she'd be snooping around, trying to find the room where the Avengers did their planning. It'd be where her memories were, but more importantly, where they kept their plans to kill.