To be overfamiliar with someone means to behave in an excessively friendly or informal way that exceeds the boundaries of the relationship. Other synonyms for this expression are to be too familiar, to be presumptuous, to take liberties, to be impertinent, to be intrusive, to be overly intimate, to be forward, to be brazen, to be bold, to be disrespectful, to be insolent, to be rude, or to be overconfident. Being overfamiliar can create discomfort and awkwardness in social situations, particularly in professional or personal relationships where formal boundaries are expected to be respected. It is important to establish clear expectations and boundaries to avoid overstepping social norms and causing offense.