Do you know the answer to this inside joke?

Question

ok so were in the car and i had this stuffed monkey on my back and he said what i had on my back in a perverted way and wouldnt tell me why he said it like that was he being retarded or is it a common inside joke?

Answer 1

having a monkey on your back is a figure of speech. like having a chip on your shoulder, but in a more positive way.

Answer 2

having "a monkey on your back" is slang for being on drugs

Answer 3

People say that they "have a monkey on their back" when they have a burden, usually an addiction, such as a heroin addiction.  Maybe that's what your friend was joking about.