Parents who constantly go out drinking every other day or every weekend. Their friends most likely also party parents or partiers, gather 'round and drink until the morning hours. Party parents most likely have a well paying job, nice house, and definitely kids. Some party parents don't pay much attention to their sons and daughters because the would rather go drinking with their friends.
Kid: "Hey you wanna come over tonight?"
Kid 2: "Nah, I can't, I have to watch my little brother."