[account42]

You could probably get away with banning all common english words as usernames if you wanted to.

[teddyh]

Even if you don’t ban all words, there are some you should filter:

• <https://ldpreload.com/blog/names-to-reserve>

• <https://xkcd.com/1963/>

[nkrisc]

Or put all user pages under some top level path and then you never need to ban anything as this problem becomes completely moot.

[datawars]

Until you invent a product or concept name that is taken by one of the users ;-)

[account42]

In that case it's not really different if the usernames are prefixed to be clearly identifiable as usernames - most companies still wouldn't want any user accounts that look like official company accounts.