Oh, wow, I have to go way back for this one.
My internet name is usually Lyralio.
The "Lyra" part came from Lyra Vulpictor, a Sonic fancharacter and persona I created waaaaay back in 2003, who by 2006 looked like this:
The "Lio" part was from a failed attempt at creating a new internet nickname. I was thinking of changing my name to LioCoyote, and I did use it at least in one online game, and while it never stuck, I did like how "Lio" sounded. It reminded me of Leonardo from the Ninja Turtles and Lucario, my favorite turtle and Pokémon respectively.
So eventually I just mashed the two together and got Lyralio.
Fun fact: I pronounce "Lyra" differently in English ("Lai-ra") and Portuguese ("Lee-rah").
Moving on, around the time I joined the TP I was getting tired of the Lyralio nickname, and wanted to try something different. So I went with just "Lio", but, judging the MLP franchise's love of princesses, I figured it'd be interesting to offset the gender neutrality of the name by adding "Princess" to the mix. And thus PrincessLio was born!
If it was now, I'd probably call myself PrincessLyra instead, since it's the name I've been using the longest and the one I identify with the most. Buuuuut if I did that, I'd probably be creating a completely different image in people's heads whenever they read my nickname. I mean, how many of you just imagined Lyra Heartstrings with wings right now? ...Yup.