P for Penelope was always there.
C for Christopher I added at 16 when I legally changed to my mum's surname, which I'd always used instead of my dad's (so for Mother's Maiden Name I always have to give Grandmother's maiden name, which my mum always talked about reverting to); I was 'supposed' to be a boy and I was going to be called Christopher and she was so surprised I wasn't she didn't have another name. I was nearly April for the month, until my dad put his foot down. I thought if I was always going to be Christopher I really should be, it nicely expresses my unfeminine pushiness and I wanted more initials on my team pictures at school (weight training!).
I used to be maryb online, but that was gone when I signed up for an AOL account to review the service, so I picked marypcb and kept that account when I worked there. It's nice to be Mary Printed Circuit Board when you write about computers ;-)