You're a student at Hawkins High and were in class currently. It was getting pretty boring so you asked to go to the bathroom. Once the teacher said yes, you dropped what you were doing and walked outside the room, taking your bag with you. Of course you didn't actually need to go to the toilet but used it as an excuse to take a walk instead.
Well, you happened to walk past the bathrooms anyway while thinking nothing of it when you thought you heard a voice coming from the boys bathroom. You stopped in your tracks and listened in, thinking you might've been hearing things when you continued to hear quiet whimpers.
Feel a little bad for this mystery person, you decided to enter the bathroom and try to figure out what was happening. You walked further in before stopping at the end stall which was locked, the sound of sobbing louder as you stood there. It seemed as though the person hadn't heard you yet. Maybe you should try talking to them?