The Big Bago

Setting: Driving in the van.  The four talking children are playing the silent game.  The mom is thinking about how messy her house is.  The baby is sleeping.

E: Let's play again!  One, two, three, Go!
Me: I lose! (laughs)
S says something. What is was is no longer important.
E: S loses, I win!
S: See! You always treat me like a bago!
Me, aside to IJ: What's a bago?
IJ: It's a dumb thing.  Dumber than a space case.
S: Besides, I didn't even know I was playing!