The process of a girl gargling cum while sucking your balls post blowjob.
The word Flagengackle comes from the lack of the girls ability to pronounce and enunciate words during this act.
Guy 1: What happened to you last night?
Guy 2: I ended up going home with Elise.
Guy 1: How did that go?
Guy 2: Let's just say it ended with a flagengackle.
Guy 1: Damn that girl's crazy.