To kill the monkey

Posted by Miri Barak on April 03, 2003

"I tell you boys, when I get home I scrub myself from top to bottom... to kill the monkey (jowls).

Does anyone have a clue to the meaning of the expression to kill the monkey, and the jowls' thing?
is it a slang, or an expression?
Thank you very much

The text is taken from an Irish movie "saltwater".