Episode 4 of "Buffy, the Vampire Slayer"
s01e04 Teacher's Pet
Title: Teacher's Pet
Original Air Date: 03/25/1997 on WB
Director: Bruce Seth Green
Writer: David Greenwalt
Guest Stars: Ken Lerner (Principal Flutie), William Monaghan (Dr. Gregory), Michael Ross Verona (Teacher), Jack Knight (Homeless guy), Musetta Vander (Miss Natalie French), Jackson Price (Blaine), Jean Speegle Howard (real Miss French)
Plot Outline:
When Xander and most of the male population of Sunnydale High fall for the substitute science teacher Miss French, Buffy tries to warn him that she may not be what she seems when she sees the well-proportioned female specimen scare off a vampire.