Hey Dubdub -

I would have said that a mondegreen is a misheard word or phrase - and a malapropism is a misused word or phrase.

Didn't I just start a thread about malapropisms not so very long ago?! [grumble-e]

but to add to this one, rather than that one:

One of my housemates during my university years used to say, to indicate that she didn't care about something, "That's no shirt off my back."