"Have someone pegged" is a phrase commonly used to mean that you have understood someone's character or behavior very well. However, there are several synonyms you can use instead of this phrase. For instance, you can say that you have someone "figured out," "sussed out," or "understood." These phrases carry the same connotation as "have someone pegged." Additionally, you can use the phrases "know someone like a book," "read someone like a cheap novel," or "see through someone" as synonyms for this phrase. Overall, having several synonyms for "have someone pegged" is useful as it helps to ensure variety in your writing or speech while conveying the same message.