Rhubarb rhubarb rhubarb
Some Ask Metafilter threads:
Where we learn from user jozxyqk that…
In college, [he] took a film class; one of the professors had been an extra in a film when he was a child.
He gave the anecdote that, when they were supposed to be “generically chatting”, they were given the instruction to say “rhubarb rhubarb rhubarb rhubarb…”
This was British English.. but still, a crowd of people repeating the word “rhubarb” was pretty convincing.