well, I chose the username that I frequently used on another board that I joined several years ago. It makes it easy to remember because I have sooo many user names floating around for different websites.

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'lirpa'--the 1st part of my username-- is simply my first name spelled backwards: april. This was a nickname of mine when I was a kid. My friends and I had this little game where we would try to pronounce everything backwards, including our names. Everyone had their own "backwards name", but for some reason mine really stuck, and people called me that all the way through high school.
The last part of my user name is '23' is simply the age I was when I started using that username. sigh--that was a few years ago, although I would love for that age to really be as permanent as my username. Anyway, I'm 28 years old now, so it does seem odd that my username has '23' in it.