Discord is bad at this. When you receive an invitation to a server, you're presented with a textbox that reads "What should everyone call you?" and you're unknowingly creating a new account. Then you're asked your birth date and then for your email. You type your email and it's already used, obviously. By this point you don't want to go through the whole process of deleting your browser history to log into your exist…
The reason it happened is b/c I use email aliases for stuff I sign up for, and sometimes I forget them...