To teenie: To act like a teenie. Most likely jumping up and down and squealing, often waving hands around. Can also involve hugging and/or dancing. Imagine a teenie being told their object of affection (famous person) is coming to their house. Yeah, like that.
Not only teenies can teenie. I, for one, have been getting very good at it. Also known as fangirling. See teenie and fangirl to understand the concept.
To teenie, to be teenying, to have teenied.
Person 1: What's up with Nikki?
Person 2: She's going to see Fall Out Boy.
Person 3: Best to avoid her went she's teenying... Oh too late! *is teenied at*