All these years and Fallon still can't control himself from laughing at the camera.
I'll never understand his appeal, he always sounds to me like he's forcing a childlike charm.
Fallon represents the new male. He's an adult who acts like a child, an awkward adolescent in a middle aged man's body.
He doesn't seem like it, but Fallon is almost 40 years old. He's about the same age as Leno when he took over.
The man you are describing is not Jimmy Fallon, it's Andy Dwyer from Parks & Recreation. It's Troy Barnes from Community. Jimmy Fallon attempts to be that, and comes off as forced, obnoxious and completely unnatural. He has this weird thing where he holds his head rigidly and then moves it spastically which he does for every character he plays while mugging awkwardly to the camera.
And did you see him on SNL? Justin Timberlake's impression of him was a better version of Fallon than Fallon, and then Fallon on the other side of the stage lost it so badly he had to duck behind the game show podium for about a ten second count.