Exactly. Well, adolescents, really: People who are insulted by being considered childish because they still think they are and they don't want to be. They're trying to transition into the new role of adulthood and confusing them with their former role of child makes them insecure because they think they're failing.

They're also embarrassed by the less self-conscious actions of older people, who are less self-conscious precisely because nobody is going to mistake a 50-year-old for a child.