shake a leg

(If you speak any Cantonese at all, this kinda sorta related video is even more hilarious)

I wanted to be somewhat original with this post.
Then discovered that a few bloggers out there have already had their way with the topic I have in mind.
So much for originality (it's ALL been said or done, hasn't it?). Yet why not another go round, eh?

The subject?
Shaky leg syndrome.
I find the shaky leg topic rather intriguing, and invite your observations...

No, not this shaky leg syndrome.
Or this one.
These are serious physical afflictions which may require medical attention.

The shaky leg syndrome I'm speaking of here seems to affect many young men.
It's a semi-involuntary (?) muscle spasm of the leg when a guy is sitting.
Feet are on the ground, with the weight of one foot or both feet resting on the ball of the foot/ toes. The foot/feet rise and fall from the ball of the foot.
The rest of the leg bobs up and down. Not slow, but fast. Spastic-like.
For no apparent reason (?).

Slightly (and much older) males don't seem to display this shaking leg thing with the same frequency as teenage guys and younger (put your own connotation on 'younger', I won't touch that definition with a twisted, crusty stick) men.
The shaky leg phenomenon is not often displayed by little boys or girls, or by women.

The shaky leg syndrome can be coupled with another behaviour that young guys often practice: why it is they feel the need to hock so many loogies (go ahead, play the game on the link - it's really gross)?
I've also a theory on the loogie thing, which I refrain from sharing here - my opinion possibly straining at the (self-imposed) PG-13 rating bounds of this here blog...

So - back to shaking that leg - what up wid it?