Jonathan Mangum from Drew Carey's Improv-A-Ganza is a good example of this trope. Despite being 40, he is often thought to be the youngest performer due to his constant usage of this trope.
David Arquette, who always seems to be freebasing sugar.
He's fully capable of playing serious roles, though he's more famous in the "hyper" persona.
The Eighth, Tenth (provided he's not brooding) and Eleventh (even when he is brooding) Doctor from Doctor Who.
Kido Shinji from Kamen Rider Ryuki is almost certainly the Keet-iest of all the Kamen Rider main protagonists. (Probably for the best considering that he resides in a CrapsackBlack And Gray Morality World that has a very high death quotientup to and including Shinji himself).
Nobuta Wo Produce has the hyperactive touchy rich-boy Akira as its Keet.
Ban from Tokusou Sentai Dekaranger takes the standard anime personality for The Hero to galactic proportions. He's ultra-loud and ultra-hyperactive 24/7. He doesn't appear to be shorter than his teammates, but it's hard to tell: he never stands still long enough for one to compare height.
Jan from Juken Sentai Gekiranger. He's the purest example of this trope (that's not Shuichi). Ever.
