Apparently there was a fad for "Laughing ..." songs in ... whatever decade it was - 'twenties, 'teens? A friend of mine years ago had a couple of 78s in the genre, same tune, both from the US. The only one I can remember was called "The Laughing Coon". (Please note I'm only using the "C" word because it's part of the song title.) The only bit of lyric I can remember is "A very close communion of mustache and of curl/The other fellow's kissing the other fellow's girl!/Ha ha ha etc.". I suspect our mirthful bobby is an Anglicised version of the theme, rather than the original. Plagiarism is a perfectly good source of new songs!

Steve