Asking cause I just changed my display name from LastTrainHome to EvidencePlz and was wondering if display names are unique and exclusive once someone chooses one? Cause if that's not the case, someone else can decide to change their display name to EvidencePlz tomorrow and falsely represent me for malicious purposes, right?

30 minutes ago, EvidencePlz said:

if that's not the case, someone else can decide to change their display name to EvidencePlz tomorrow and falsely represent me for malicious purposes, right?

Touch paranoid there aren't you? Is there some reason why anyone would want to pose as you and maliciously start posting stuff?

I don't think there's anything to be concerned about. Nobody will or can have the same Username as another in the same database.
It is my understanding, having created and later changed my account username at various sites. When you create an account or change your display name (Username), the database for that site or forum will check first whether it can offer your selection of characters or wording. If what you have typed as your unique user is already in use by another member then it will reject until sufficient difference between what exists in the database and your unique username are met. There can only be one unique username for each member account. This is later confirmed by email when your user account credential needs to be confirmed, (or if changed), usually when receiving the email addressed to the account creator, you would need to visit a confirmation link (usually for a set time period) sent by the admin bot or account manager to your email address when setting up the account.
What is unclear about when a user creates a username, that is lets say, a real name (which may be valid and available, and processed to formally create that account), and another user wishes to use his/her own real name (which is spelled exactly the same as an account that already exists), it might not be available to the second person unless a character variation was used. If the first person then changes their username does that mean it then becomes available to the second user, or unavailable forever to any other user than the first person to create an account with that name and spelling.