Penny: Okay, Sheldon and Amy are still pretty upset about their theory being disproved.
Leonard: So we have made a list of subjects for everyone to avoid.
Penny: Symmetry.
Leonard: Asymmetry.
Penny: Uh, SimCity, sounds too much like symmetry.
Leonard: That also applies to The Simpsons, Simba from The Lion King, and cymbals.
Penny: Russia or Russian in any context. The country, the dressing, the roulette.