 " Sexy " is the fifteenth episode of the second season of the American musical comedy @-@ drama television series Glee , and the thirty @-@ seventh episode overall . It was written by Brad Falchuk , directed by Ryan Murphy , and first aired on the Fox network on March 8 , 2011 . The episode mainly revolves around the topics of sex and adolescent sexuality . In it , Holly Holliday ( Gwyneth Paltrow ) returns to McKinley High School as a substitute teacher in a class devoted to sex education . Glee club director Will Schuester ( Matthew Morrison ) begins to develop feelings for Holly , and guidance counselor and celibacy club advisor Emma Pillsbury ( Jayma Mays ) is less than pleased with Holly 's lessons . Santana ( Naya Rivera ) expresses her love for Brittany ( Heather Morris ) , and Burt Hummel ( Mike O 'Malley ) has a talk with his son Kurt ( Chris Colfer ) about sex . 
