Waving your bladder all over the place

The story:

It was my younger brother actually, who must have been about ten at the time. My mother was the only one to overhear his error, though you can be sure she quickly summoned the rest of the family to join in the laughter and the taunting. (In his embarrassment my brother didn't attempt any defence, but he could have argued that if the young man in the song was waving his own bladder then this would account for the 'blood on his face' as well as providing indubitable proof that he was 'hard'.)