I have to enter a username and password to log into a new WiFi network. I entered the wrong username the first time I tried to connect. The username has been grayed out every time I've tried to connect after that:

WiFi usernames are stored in config files inside /etc/NetworkManager/system-connections/ but having to enter terminal commands to edit a config file in vi just to connect to WiFi is abstrusely convoluted to most people. It's one of those things that pushes a lot of people back to Windows. :(