A tween hipster; someone between the ages of 9 and 12 trying to be a hipster.
Jonathan: Look at how these kids are dressed.
Meg: Don't make fun of them, they are like twelve.
Jonathan: NO - look at that douchbag's socks, they are hunter green, he is TRYING it look like that, like a tween hipster
Jonathan and Meg: you mean a tweepster.