Season 3: Episode 50: Nitpicking
After Dominic comes back from a sleepover party with head lice, Jimmy and Christine are so fearful of what Greg and Kim might think of them that they don't say anything. Jimmy and Christine quarantine Dominic while they treat it, but Jimmy inadvertently gives it to Sam by rubbing the kid's head after rubbing Dominic's. When Sam starts scratching, a guilt-ridden Christine confesses to Greg and Kim. The lice starts spreading like wildflower when Greg and Kim both catch it next, and Greg unknowingly gives it to Mr. Savitsky, who made him try on hats. But when Greg tries to tell Savitsky, he mistakenly thinks he was the one who gave it to Greg -- until Jimmy intervenes, that is.