Usernames.

Mine has a history. Like others I use it for everything. If FlyingPoodle or Flying_Poodle is too long, I try for just Poodle (but that gets taken more than you'd think).

I'll work backwards:
Like I said, it's the default to anything I do that requires a username and is for entertainment. For serious stuff, I just use my email.
So on League of Legends and other games I play now (I think LoL is it?) people know me as FlyingPoodle, or Poodle for short which is fine.
People think I'm a girl for some reason. Poodles are associated with women more I guess?
I first used FlyingPoodle as Flying_Poodle on Diablo 2 for my Hammerdin. It was hard naming characters on that game w/o having it taken but this stuck and I ran with it. Plus, Hammerdins was a class almost everyone had because...1 hammer = Baal dead...so I had the name a while to stick to me.

We use to have a little play poodle here. My brother use to pick it up and say "fly poodle fly." The poodle didn't like this. So when I was coming up with D2 names, he walked by and boom! FlyingPoodle