The song steve martin sang

I remember watching this movie and laughing near the end when steve martin was forced to sing a song about his Dad, and sung a funny 'tura tira rae' song.
Classic steve martin.
But I forget what led him to have to make up an inpromt song about his father to impress his boss. Can anyone enlighten me to what led him to sing that? Did he tell his boss that he wrote a song for his dad just as a lie just to impress him, resulting in him telling steve to sing it in front of everyone? What led to that scene? I forget :)