"Whatshisface" is a slang term used when someone can't remember a person's name. It's commonly used informally in conversations. In situations where it's inappropriate to use, it's better to use synonyms. There are several synonyms for "whatshisface" such as "so-and-so," "John/Jane Doe," "Mr./Ms. Anonymous," "unknown person," "mystery man/woman," and "nameless person." While all these synonyms mean a person whose name is unknown, some are considered less informal. For instance, "John/Jane Doe" is commonly used in legal situations when referring to unidentified persons. In situations where remembering someone's name is essential, avoiding the use of "whatshisface" synonyms is recommended.