Mines is pretty simple - Deoxys is my favourite Pokemon and Destiny Deoxys is my favourite Pokemon film.
It was also my Xbox Gamertag until I had to change it due to rather unfortunate circumstances...
Hmm... well my original name was TrinityOne, a move used by Kyo Kusanagi from the King of fighters series. I just shortened it to Trinity. It also represents the Imperial Regalia of Japan, or the sacred teasures...the Kusanagi no Tsuguri, the Yata no Kagami, and the Yakasani no Magatema. Hence the name Trinity.
My username is of no particular significance. I just...wanted something unique, random, memorable, and not specific to any one character or fandom, so I could use it for just about anything. And "Lawnmowergirl" fit the bill.
Short for "Your Friendly Neighborhood Guest", this name was conceived on a previous forum I was on when I was posting in the Chat Box. I posted under "Guest" since I wasn't registered at the time of conception.
I was chatting with a Mod when another Mod came on and asked, "Who's the newbie?" The Mod I had been chatting with replied, "Just your friendly neighborhood Guest." Needless to say, it stuck.
...Oh, you want to know what the hyphen's doing in there? To be honest, I don't know. Go figure.
My current internet alias, NyaChan, started off back in elementary school actually. I had these cat PJs and I decided that when I wore them I was the amazing half-cat super heroine, "Meower"! 8D My sister had dog PJs and she was my partner Pupster. So, middle school came and I made some friends who got me into anime. So I drew things, and drew what I thought Meower looked like. She separated from being myself in kitty PJs to being this blue-haired, half-cat girl. Not too long after that my house got Optimum Online and we were all allowed to get e-mails cause we could get them and they would be useful. So, amidst all the Harry Potter related names I came up with, there was "meower", which turned out to be available and thus started what I would use online to refer to myself.
After that I got an AIM account which involved "meower". Later, I decided to use "Chibi" in it as well, resulting in my DeviantArt and Gaia Online usernames. A little while after that I got into Tokyo Mew Mew and learned that "nya" is the Japanese onomatopoeia for the English "meow". I signed up at some Tokyo Mew Mew site and wanted to use "nya" in my name. Of course "Nya" felt too short, so I put in the suffix "-chan" to make it "Nya-chan".
Much later, I came across some site that didn't like hyphens. So at that point I dropped the hyphen and chose to capitalize it as "NyaChan". And that's it. When "NyaChan" is taken, I use "NyaronChan", referencing "nyoron~" from Churuya.