This was inspired by a documentary I’ve just watched on BBC 4 about the song ‘Fairytale of New York’ by the Pogues and Kirsty MacColl (well worth a look if you have the time).
In British slang scumbag just means a horrible person. But in US slang it means condom. Yep. It comes from ‘scum’ which is US slang for ‘semen’ and ‘bag’ which means, well, ‘bag’. So, there you go.