This occurs when a male collects a large quantity of his own ejaculate in one large container (the Mary Poppins Bag). A common use of the Mary Poppins Bag is to be tossed into an unexpecting female during their gynecology appointment - exploding on impact.
Erik: (casually) Yo I just gave Lindsay my fat 'Mary Poppins Bag' on Wednesday.
John: (disgusted) You are actually a disgusting human being... (Curious) Did you film it?
"Poppins" was a word from 'old-time' English, removed from the dictionary by the US Government in a conspiracy against the native English Language. It was once used as an adjective, and described pleasurable or nice things.
"I just got a waxymiggins off some chick last night, it was totally poppins!"
Jackson: "Did you see the film last night?"
Jon: "Yeah, it was totally poppins!"