I think this goes a bit further than bodhran and banjo jokes...

Hiromi Lorraine Sakata, Music in the Mind: the Concepts of of Music and Musician in Afghanistan, pp.78-9, describes how some kinds of music are mainly played by barbers, who are a tabooed, outcast group marrying within themselves and buried outside the walls of the cemetery. Barbers also conduct minor surgery and circumcisions. Their characteristic instruments are the sorna and dohl - i.e. shawm and bass drum - and players of these instruments end up in the same social category as barbers. It seems they owe their degraded social position to being a migrant lower-caste group from India.

Perhaps the exclusion of sorna and dohl players can be explained by the instruments' supposedly polluting qualities. The double reed of the sorna is placed entirely within the mouth of the player; thus, the reed and by extension the whole instrument is contaminated by the player's own spittle. Spit is likened to semen by the gypsies, an idea suggested by our own expression, "he is the spitting image of his father". This polluting attribute is supported and sustained by stories and notions of the evil, satanic origin of the sorna. It is considered by some to be "the penis of Satan", and the first maker, performer and teacher of the sorna was said to be the devil himself. According to a Herat folksong, the skin for the dohl is made out of a donkey's stomach and the sorna is made out of its penis.