When someone says a word that is superficially similar to, but means something different from, what they really mean, we call it a malapropism. I'm looking for the counterpart to this—a word for the act of wrongly interpreting a correctly spoken or written word.
When the problem is purely acoustic, as in this example:
OLD GEEZER #1: It's windy today!
OLD GEEZER #2: No, it's Thursday.
OLD GEEZER #3: Me too! Let's get a drink.
One example might be from Stanley Holloway's 1931 monologue "The Recumbent Posture" in which the instructions on Albert's bottle of medicine dictate that it is to be taken "in a recumbent posture" leading to his parents scouring the town to find such an object.
Of course, sometimes it can be done deliberately:
MRS FUSSEY: Joan may think you're a gentleman but personally I've got sore misgivings.
SID BOGGLE: You ought to put some talcum powder on them.
(Carry on Camping, 1969)