The Big Bang Theory Season 1 Episode 11 : The Pancake Batter Anomaly
Penny returns from visiting family in Nebraska and as she picks up her mail from Leonard, she mentions most of her relatives got sick. Sheldon freaks out as, according to Leonard, he is a germophobe. Sure enough, Sheldon becomes sick and instantly becomes the biggest pain possible. As it's evident this has happened before, Leonard and the guys hide from him at a Planet of the Apes marathon, leaving Penny unwillingly to take care of Sheldon. However, Leonard accidentally breaks his glasses and must re-enter the apartment, as he is almost blind without them; Penny catches him and sticks him with Sheldon. As he tries to escape after her, he runs headlong into a wall and nearly knocks himself out. In the end, both Leonard and Sheldon are sitting sick and injured on the couch.