The term "manchild" refers to a grown man who displays childish behavior. For those who find the term offensive, there are several synonyms that can be used in its place. One such word is "immature man," which conveys the same meaning without the negative connotations. "Peter Pan" and "eternal boy" are also frequently used to describe men who never seem to grow up. Another option is "adolescent adult," emphasizing the individual's stunted development. Terms like "big baby" or "spoiled brat" may also be used to describe such individuals. Ultimately, the choice of synonym depends on the specific context and intended tone of the conversation.