Dads friend
A guy who uses the excuse of being 'Dad's friend' to sneak out of a party and go somewhere private to do his business.
"He said he had to go talk to Dad's friend. I know he was going to smoke weed."
"He left the party to go find Dad's friend. I know he was going to masturbate."
"He said he needed to go see Dad's friend, but I think he just wanted to be alone."