CBS

Season 2: Episode 11 - The Bath Item Gift Hypothesis

The Bath Item Gift Hypothesis: Leonard meets his intellectual superior in award winning scientist David Underhill. Underhill is the total opposite of Leonard: handsome, charming, and cool. He's the whole package of brains and looks which initially doesn't sit well with Leonard. Although when Hill asks for Leornard's help in research he is undertaking, he happily jumps at the offer. Leonard's joy of working with Hill is hampered by jealousy when Underhill takes an interest in Penny and the feelings are reciprocated.

Sheldon, having always viewed the holidays as a pagan ritual that is rooted in obligations rather than holiday cheer, is taken for a loop when Penny brings him a Christmas gift. He now feels obligated to buy her a gift and enlists Wolowitz and Koothrappali to help him with this task which they reluctantly agree to. Sheldon believes he has come up with the most logical gift giving scenario until he opens Penny's gift; he cannot believe what she got him.