“Everyone was doing it” stops helping the second you’re the one who got caught.

Shared behaviour feels like shared responsibility right up to the moment consequences get handed out, and then it turns individual. The teacher, the manager or the officer is dealing with you, and the number of other people involved does not reduce your part of it. The crowd was real and it was never a defence.

Notice when the number of participants is doing the work your own judgement should be doing. Ask what you would say if you alone were asked about it tomorrow. If that answer is thin, step out quietly, without needing to persuade anyone else to come with you.