The Big Bang Theory Season 1 Episode 10 : The Loobenfeld Decay

Penny is given a part in Rent, though after hearing her sing extremely off-key Leonard lies to avoid seeing her performance so he won't hurt her feelings. Sheldon becomes worried that Leonard's lie was not good enough, so he creates an intricate lie about his non-existent drug addicted cousin "Leopold Houston", who was in need of an intervention (and thus why they could not see the play). Sheldon becomes so obsessed with the credibility of his li...