S4E7: Promortyus

In "Rick and Morty" Season 4, Episode 7, titled "Promortyus," the episode wraps up with Rick and Morty escaping from the alien planet inhabited by the face-hugging parasites called Glorzo. After blowing up the Glorzo headquarters and inadvertently killing off the entire parasite civilization, they make their way back to Earth. They return to find Summer has been chilling in their spaceship's glove compartment, having avoided getting a face-hugger herself. Summer explains that she actually caused all the chaos by encouraging the Glorzo to live their lives to the fullest, which led to their downfall. The episode concludes with Rick and Morty feeling guilty about having wiped out an entire species again. But of course, true to form, they quickly brush it off and rationalize it away as just another bizarre adventure. They head home, leaving behind the mess they created without a second thought.