"When Worlds Collide" is a rap song performed by Robot X-29488 (voiced by Tom Kenny) and Cavey (played by Bill Fagerbakke) in the episode "Ugh." It is also featured in The Yellow Album.
Lyrics:
Robot: When worlds collide...
You can run...
Cavey: But you can't hide!
Robot: When worlds collide
You'll laugh so hard you'll swear you died
When worlds collide
Hold my hand and I'll be your guide
When worlds collide
Buckle... buckle...Buckle up for the sweetest ride
And prepare to have your mind blown wide
When worlds collide
Cavey: When worlds collide it's a curious thing
Bet you've never heard a robot and a caveman sing
In his metal chest are some working parts
How is that different from my beating heart?
Robot: I'm from the future...
Cavey: ...And I'm from the past
Robot: But that don't mean this friendship wasn't built to last
Cavey: He was made in a lab and I was born in a cave
So let me hear you holler for this inter-era rave!
Robot: You... you... you... you can run...
Cavey: But you can't hide!
Robot: When... when worlds collide.