One who runs around with high energy and no real purpose. A hyperactive person.
A person who is being overly stimulated, over excited or out of control of their emotions to the point of it being obnoxious to those around them.
A person who is completely agro or out of control.
Tom: Yeah man! I can't wait to for the concert tonight, it'll be so awesome!, I can't wait, can't wait, can't wait!!
Carl: Dude, don't go getting all "Billy Barty" on my ass.