(Penny explains to others what not to say infront of Amy and Sheldon to not make them upset...)

Penny Hofstadter: We should just try and avoid anything that makes them think of their project or science or Nobel Prizes or successes or failures.

(Amy and Sheldon walk in...)

Amy Farrah Fowler: What are you guys doing?

Bernadette Rostenkowski-Wolowitz: Nothing.

Sheldon Cooper: Nothing? Like what my career has come to? Thanks a lot.

(Sheldon storms out of the room)

Howard Wolowitz: Nice going.