I hear a bum that whistles
and I have balls that sing

The story:

I got some humble pie square in my face when I proudly pointed out to a college friend what I "knew" the right words were. He told me what they actually were & proceeded to laugh horrendously & let the rest of the dorm know that I had "balls that sing". But it backfired on him when they asked him how he knew so much about my balls.