"Who're you callin' a dummy, dummy?" is a phrase imagined as the only piece of dialogue spoken between two dummies. It was created primarily by Ben and secondarily by Fraser in Part 7 of the Assassin's Creed II long-haul, inspired by the training dummies in Leonardo da Vinci's backyard. Two dummies are to be imagined as speaking to each other, one saying to the other "Who're you callin' a dummy, dummy?", prompting the other to respond "Who're you callin' a dummy, dummy?", ad infinitum. Fraser admitted he could imagine watching this go on for a long time.
During the long-haul of Phoenix Wright: Justice for All, Fraser revealed that he and Ben had been thinking of a scenario involving both of them in a ventriloquist's act, with Fraser as the ventriloquist and Ben as the dummy, where they would say the line to each other in turn.
The joke sometimes comes up when dummies are involved or spoken about, or when the word "dummy" is mentioned. In the playthrough of New Super Mario Bros. U the joke went so far that Fraser and Ben broke down into hysterical giggles, to the point where Fraser couldn't even speak properly anymore.