inverted pushpop

The act of inserting a non-erect penis into a vagina then having it becomes erect inside said vagina to give a push pop feeling

Person 1: "I didn't get it up in time so I just put it in flaccid."
Person 2: "How did it feel?"
Person 1: "Like a push pop just the other way around."
Person 2: "So an inverted pushpop?"