Remember seeing this in the foreword of a book of Asimov's favorite limericks:
It was, in truth, an eager youth
Who halted me one day.
He gazed in bliss at me, and this
Is what he had to say:
"Why, mazel tov, it's Asimov,
A blessing on your head!
For many a year, I've lived in fear
That you were long since dead.
Or if alive, one fifty-five
Cold years had passed you by,
And left you weak, with poor physique,
Thin hair and rheumy eye.
For sure enough, I've read your stuff
Since I was but a lad
And couldn't spell or hardly tell
The good yarns from the bad.
My father, too, was reading you
Before he met my Ma.
For you he earned, once he had learned
About you from _his_ Pa.
Since time began, you wondrous man,
My ansestors did love
That s.f. dean and writing machine
The aged Asimov."
I'd had my fill. I said: "Be still!
I've kept my old-time spark.
My step is light, my eye is bright,
My hair is thick and dark."
His smile, in brief, spelled disbelief,
So this is what I did;
I scowled, you know, and with one blow,
I killed that rotten kid.