This tutorial assumes you've already logged in to phpBB
Now let's learn how to disallow usernames
1) Click Users and Groups
2) Click Disallow names
3) Enter a name you wish to disallow here
4) Click Submit
That's it! The name StoreHater can no longer be used in the forums
Now let's remove it from the list so it can be used once again. Scroll down
5) In the Remove a Disallowed username section, click Submit
The name is now allowed to be used again
This is the end of the tutorial. You now know how to disallow usernames in phpBB