<p>Yes, dealing with 2 accounts on one computer is pretty tricky and requires constant use of log-out. The good idea here is to use browser's "porn mode" (Incognito/Private/InPrivate depending on browser) --- this way you can remain logged in normal mode while your friend can simultaneously operate in the incognito one.</p>

<p>Going back to your problem, this is something you can fix on your own; just use "my logins" tab in the profile page to remove your OpenID from the friend's account so you can use it to create a new account for you. <a href="https://stats.stackexchange.com/help/edit-logins">Here is an official support page about this</a>.</p>
