Even those who've never suffered from backacne should immediately understand what it is from it's use in context.
Two syllables, and is often mis-heard in advertisements for arthritis nostrums: "...to cure back, knee, hip, and joint pain."
Flavor Flav had backacne,
just ask James Cagney,
he beat up on a guy
when they found he was a fag-ny.
(sung to "Letter To The New York Post" by 'Public Enemy')