The 'monkey' idea has been an indication of contempt for a long time as in "to make a monkey out of" someone etc. The version you ask about often has a very crude addition such as the f-word. This just adds to the effect of ensuring the listener knows the idea is that you do not care at all. It's quite recent, in fact, being recorded nowhere prior to the 1960s.
(Anyone who is convinced he was saying it in 1945....please contact The Oxford Englis Dictionary with your evidence!)