A person of the Muslim faith lacking all common sense. A Muslim who displays signs of tardity.
A combination of the word "Muslim" (A believer in Islam who refuses to integrate into American society) and the word "tard" (to delay). Therefore, a muztard is an object of ridicule for two reasons.
Emily: Dude, why is your new roommate standing outside in the rain wearing a sheet?
Brad: Didn't you know, he's muztard.