O melhor dia preguiçoso de todos os tempos

Temporada 1, Episódio 28.

Da wikia:

Phineas and Ferb decide to do absolutely nothing for the day. Candace questions her purpose in life after realizing that she can't bust her brothers for doing nothing. Meanwhile, Dr. Doofenshmirtz is tired of being the ugliest person around, so he invents a device that can turn anything and anyone ugly.

A partir da transcrição :

Phineas: You know, Ferb, everyday we do something really big. But you know the one thing we haven't done? Relax. I say we take advantage of this perfect day and have the best do-nothing day ever.

Aqui está um link do YouTube, se você quiser assisti-lo: