name of a song and episode

Anyone know the name of a song and episode where the three were playing around in a park and a song was playing..it was something along the lines like we're having some fuuuuuuuuuuuuuuuun were gonna have fun fun fun fun fun?LOL anyone know what i'm talking about?

You want to play the game, you'd better know the rules, love.
-Harry Callahan