When it comes to describing the lack of sincerity or genuineness in someone's behavior, there are several synonyms for the word "insincerities". One alternative could be "hypocrisies", which refers to deceptive or feigned actions. Another synonym is "duplicity", highlighting a person's deceitfulness or deceitful nature. "Dishonesty" can also be used to convey insincerity, highlighting a lack of truthfulness or trustworthiness. Additionally, "pretenses" or "falsehoods" are suitable synonyms, emphasizing behavior that is not authentic or genuine. These synonyms capture the essence of insincerities, conveying different shades of dishonesty and lack of genuineness in individuals' actions and words.