The Big Bang Theory: Season 1, Episode 16

1 - 16: The Peanut Reaction

When the men dine at Penny's restaurant, she finds out that Leonard has never had a birthday party, as his parents didn't believe in celebrating anything but achievements. She decides to throw him a surprise party, and blackmails Sheldon to join her. However, when the day of the party arrives, Penny finds Sheldon did not buy a birthday gift, so she has to drive him to a computer store to pick up a present. Meanwhile, Howard is in charge of keeping Leonard out of his apartment until the party. Howard pretends to eat a peanut bar, to which he is allergic, so Leonard can drive him to the emergency room. However, due to Sheldon's absent-mindedness in the computer store, Howard has to keep Leonard distracted even longer, and he is forced to actually eat the peanut bar, causing him to swell up in a severe allergic reaction.