Being in a state of utter excitement (noun or adjective). Can be facially expressed by protruding your lower jaw as far as you can, and smiling at the same time, while squeezing your hands (as though you are "gushing" something)
Daisy: Lizzie aren't you so gushay right now?
Lizzie: YEAH! GUSHAY!!!!!
Lizzie: Come gush my fat belly.