Robin Williams mixes his comedy routine with the song "Those Were The Days" by Gene Raskin, added life and death and called it "The Grim Rapper." It's included with Live 2002 on the bonus CD (filmed on Broadway). If you like the skit, then buy the CD or DVD it's hilarious. I'll provide more details on the song (if I can find the CD), clean up the lyrics and add captions soon, hopefully.

[HD] Available [CC] Coming Soon (Too lazy for time stamps right now)

Lyrics (Rough Draft for now):
maybe it's not the Grim Reaper
maybe it's the Grim Rapper
maybe it's just some guy that comes for ya
and goes like ya know
yo yo yo
it's time ta go
you've lost all your fluids
your vitals sapped
time to get ready fo a big dirt nap
i'm tellin' ya this with all my heart
you've had it from the beginning from the very start
whether you're going down below
or whether you're going up above
there's only one thing that you got to know
only one thing that matters
those were the days my friend
we thought they'd never end
we'd sing and dance forever and a day
we'd live the life we choose
we'd fight and never lose
for we were young and sure to have our way
when you're 16 you're invincible
when you're 18 you're invincible and you every fucking thing
you're in love for the first time
i'm in love
it's over
ican't live without Susan
but wait there's Becky
those were the days my friend
we thought they'd never end (i am gonna change the world, i am gonna change the world)
for we were young and sure to have our way (but first I'm gonna get a job)
then on to 18 where your like there is nothing like death
maybe someone dies but it's freaky shit
like a friend dies when you're 18
it's like aw fuck dude, car wreck
but I'm still invincible
and then you get to be 20
and it's like not only are you invincible
you can get loaded for the first time and be really an asshole
going aw man I'm invicibleeeeeeeh
those were the days my friend
we thought they'd never end
we'd sing and dance forever and a day (yo yo)
we'd live the life we choose (it's the drugs man)
we'd fight and never lose (im glad ive kicked, im off that now)
for we were young and sure to have our way
well maybe i'll have just one last ok just hit i'm ok hehehe
you know i'll quit it when i'm 30
then finally you hit 30
and another coupla friends die and you go oooh shit
can't be doing blow and have a kid
because you'll be going daddy wants to play
it's 4 o'clock in the morning wanna play with daddy
and the judge said alimony
but he really meant all the money
and it's ok and it's alright and it's was like
you know it's ok you'll get you'll gain it back
and then a ena friend dies of a heart attack
and you're like doc just put your finger in my ass ok
yeah do the complete mri that's good
blood, urine, stool just take my underwear
here ya go there ya go um
and then ya get 50 and then your parents start to die
those were the days my friend
we thought they'd never end (now im an orphan and im fucking 50)
we'd fight and never lose
for we were young and sure to have our way
and you hit 60 and then go beyond
and maybe you hit 70
and you're looking around going oh gah i remeh i remem ah
what's your name
and then you get 80 ah 90 and ah 80
you're still good you're still good
you're still vital the golden years
a lot of people going yeah a little tarnished but gold
is there sex in heaven (no)
those were the days my friend(yo yo yo youre coming with me now)
we thought they'd never end (seeing how ya feelin and ya know somehow)
we'd sing and dance forever and a day (i'm gonna take ya down without a sound gonna bury your ass in the ground)
we'd live the life we choose (put out put away)
we'd fight and never lose (come on and say life is ova ya got ta pay)
for we were young and sure to have our way (let ya soul fly up let your heart be free)
come on now baby you're comin' wit me
take care of yourself