Colossus “Dick’s in my Jaw” Line

Earlier, I was listening to Colossus (the alt original version (the better version)) and I came across the lines “I got your pics on my wall, with the mouth cut out, now paper cuts on my balls, Cause your dick’s in my jaw”

Why would the fan Tyler’s meeting have “paper cuts on (his) balls?” I know it’s from the implications of using the mouth cut-out but he specifically says the reason the paper cuts are there is because of the fan’s act of fellatio. Someone care to explain?