We don't really have one, although I can think of a few when they are misbehaving! My DS10 picked one up from my DS11's 4th grade class for some reason. When we went in to pick DS11 one time, a couple of kids called him "Pinata". He hates it of course, but every once it a while DH will refer to him as that w/o letting him hear.
I used to call DS11 "Doodlebug" when he was a baby.
Of course when she's misbehaving I call her "sunshine". One day we were in Disney waiting for the rest of our party to get off of Rockin Roller Coaster and she was cranky. She was really hungry but refusing to eat no matter what I offered. So I made some kind of comment and ended it with her pet name "sunshine". She spun and asked "Why do you call me that?" with attitude. So I just responded "Because if I called you what I really wanted to call you I would get in trouble." The cast member that overheard me had to put his hand over his mouth and turn around he was laughing so hard.
My dd's name is Caitlin and I've always called her Caitie Cat. She's 19 and she must still like it because she has it on her signature line of her text messages.
I've called Mike "Mickey Mouse" since he was a little baby! Now he's twice my size and I still kiss his cheek while he's sleeping and call him "Mommy's lil Mickey Mouse"....
When my DS12 was born I started calling him pumpkin doodle, thank goodness that one didn't stick! I also sometimes call him Tyler Bear. Sort of like calling him teddybear.
Some how my DS8 got the nickname Nader (name is Nathan) from the guy that use to babysit while I was in a spinning class.
Our DD2, we call her Boogins. That's evolved into several "sub-nicknames" such as Boogity, Boogs, or Boogie.
When our second DD was born, she held her hands in fists ALL THE TIME. We were laughing about how she had her "Dukes" up, which evolved in to Amy-Dukes, Dukes, or Dukeys.
DD has always been petite but spunky so we call her Pixie or Pix
DSis and I have always had this silly thing where we call each other Grasshopper when we are right about something, When DD was little she wanted to be called something so DSis calls her Cricket which she loves.
Yeah. That is where Cissy comes from too. Bubba if you couldn't say brother and Cissy if you couldn't say sister.
My grandmother and her sisters all had nicknames that they went by all the time. Grandmother's name was Willard. Yeah, they thought she was going to be a boy. She was called Bill her whole life. Her sisters were Pete and Dock.
DS was called Possum from day one. He is 19 now. I called him Possum for 2 reasons. First off he loved to hang upside down. Also, when you thought he had fallen asleep in your arms and put him to bed, as soon as his back hit the mattress he woke up. Of course when he is being ugly I call him Ungrateful Little Snot. He really hates that, LOL.
We have a few names that WE call the kids:
DS23 Big Buddy, DD16 Pretty Girl, and DS14 Little Buddy, Mama's Buddy, or Big Boy.
My kids have beautiful names that we really studied over before we chose them--John George Christopher, Eleni Catherine Georgette and Christian Thomas George. Yet, they called each other Brubba, Nay-Nay, and Shishen. So much for that!