I notice people have their own forum title like they made up their own on the bottom of their username. I was wondering how you do that?

A lot of forum titles come from various achievements as prizes. To change your own forum title:

Go to Preferences - Forum Options - Change Forum Title

Or go here: http://subeta.net/preferences.php?act=forum&change=title

And if you're missing any titles:

Go here: http://subeta.net/achievements.php/claim_titles

But how is yours "is a worthy opponent"?

It's an achievement prize: Tie at a game of Mazes & Mahars!

Here is a list of forum titles with the achievements that they correspond to. This way, it's easier to find one you like to try to complete the achievement for it. (:

Some of them are retired though, which means they're no longer available.

Thank you so much that helps a lot :)