My girlfriend thought she was being funny when signing up with a username that goes along the lines of firstname.lastname@example.org. Yes, she wrote that as the username. Don't ask me why. She was smart enough to put a valid e-mail address in the correct field though.
So far I haven't encountered any other issues than not being to able to add her account with the username as the server probably recognizes is as an e-mail address.
Edited by Mannerheim, 05 November 2019 - 05:10 PM.