IPA: /ˌoʊvərfəˈmɪljər/
KK: /oʊvərfəmɪljər/
Excessively friendly or informal, often to the point of being disrespectful or inappropriate.
His overfamiliar behavior made everyone uncomfortable at the meeting.
Overfamiliar → It is formed from "over-" (meaning excessively) and "familiar" (from Latin "familiaris", meaning of a household or intimate). The word "overfamiliar" means excessively familiar or too intimate, often in a way that is inappropriate.
Think of being 'excessively' ('over-') close or 'intimate' ('familiar') with someone, which helps you remember that 'overfamiliar' means being too familiar.