Show username in Thread Title

[TheFrienzNet]

I am using the Form Hack and I wanted to do something that shows the username when we submit so it shows up like this:

Username - Moderator Application

But I can't seem to get it right, I always get - Moderator application (without the name)

Here's my code:

PHP Code:

////////////////////////////////////////////////////////////////////////////////////////////////////
//TITLE OF THREAD/POST/PM/EMAIL (do not use quotation marks in the title or you will get a parse error)
//You may use variables from the form for this.
////////////////////////////////////////////////////////////////////////////////////////////////////

$posttitle = "$bbuserinfo[username] - Moderator Application"; 


I also tried $userinfo[username] but no luck. I'd appreciate any help!