"If You Do It" is a song sung by Shary Bobbins in "Simpsoncalifragilisticexpiala(Annoyed Grunt)cious"
Shary is serving the Simpsons family dinner in the living room. Bart and Homer are being difficult and want Shary to wait on them hand and foot. To motivate them to do things on their own she sings this song.
The lyrics are: If there is a job that must be done
You'll find it much more fun
(Homer interrupts and says "You'll find it's even more fun if you get it for me.")
But the beer will taste more sweet if you get up off your feet...
(Bart interrupts Shary and says "Lady, the man asked for a beer not a song)