To kill the monkey

"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".

the "jowls" bit might be to describe the action of stroking an imaginary beard which is a way of casting doubt upon the truth of what you yourself are saying. the gesture is also called to "chinny" and th emost popular version I heard was "chinny reckon" pronounced 'reck-on' - i.e. I do not believe/agree with you. There is also a gesture used in the deaf speech (British Sign Language (BSL)) which has they same meaning.

In the context, your quote might have meant that he said he was going to scrub himself but was not intending to do so. The kill the monkey expression could be a euphemism for masturbating as in "choke the chicken" - something not entirely unknown to take place in showers.