To "fistbomb" a group, is to turn the topic of discussion towards the sexual practice of "fisting", then to leave the group, while the discussion continues in an inescapable cycle that no-one wants to continue but no-one has the power to stop.
Jack: "which really ended their careers in 70's".
Andrew: "You know what started in the 70's, fisting. Before that the practice was highly unpopular and rarely document".
Ann: "What's fisting"
Andrew leaves, fistbombing run successful.