Correction Appended: May 19, 2011
There's a particular type of man who, as soon as he starts to get a little tipsy, wants to sing. That's not to say that he has a great voice or even remembers all the lyrics, but he wants to sing and sing he will. Apparently, Maverick and Goose are two of those men. In this scene, the pair show Goose's boy how fun it is to drink in the middle of the day. It also introduced young children of the '80s to the greatness of Jerry Lee Lewis. (Sadly, in 2008, the bar where this was filmed — a San Diego joint named Kansas City Barbeque — burned down. The piano, however, survived and it has since reopened.)
Correction: The original version of this story stated that Kansas City Barbeque's piano was lost in the fire.