I thought you were kidding so I checked and found another meaning: :)
avere una scimmia addosso= essere ubriaco o fatto di droga (to be drunk or on drugs)
It's the same; "scimmia." The word is feminine, therefore you must use "una", but it applies to both genders. Have a nice day! :)
Once again, I am having trouble pronouncing "Io ho __" - is it EE-YO OH OO-NA SCIMMMIA? Or is it EE-OH OH OO-NA SCIMMIA? Or EE-YO OHOO-NA SCIMMIA?