This is a good reminder that forcing people to use an E-mail address as a user ID is a stupid and dangerous policy. Voted down by amateurs who set their Web apps up this way. Killing the messenger won't secure your users' credentials.
As if users wouldn't just use the same username everywhere. So now besides telling them to use different passwords for every website, you also need to tell them to use different usernames.
But you can't use the same username everywhere, for example doing a Google search of my username shows accounts on other sites that are not related to me. Doing a search for your username suggests that it is also likely taken on numerous other sites, including a rock-band named FoxyGen that I'm fairly confident you are not a member of.