Subverting the old joke, this character really was born yesterday, or this week at least, either artificially aged or just plain made the age they are now. They tend not to understand slang, or much of anything else, and will misunderstand social rules with usually comic results. May also be the result of a person being born normally but kept in some kind of stasis and never being conscious during their development since they still awake as a 'new' person. Examples