 The pilot episode, "Welcome to the Hellmouth/The Harvest," ends with  Buffy, Willow, and Xander joking about the possible ways Buffy could  get kicked out of school, and Giles sighing, "The Earth is doomed."  The last episode, "The Chosen," contains a scene near the end where  the three kids plan a trip to the mall and Giles sighs, "The Earth  is definitely doomed."