Overly familiar; too casual or forward in behavior — lacking proper distance or manners. Often negative when used toward strangers or superiors.
初対面なのに馴れ馴れしく話しかけられて不快だった。
I felt uncomfortable because someone I had just met spoke to me too familiarly.
彼の馴れ馴れしい態度に周りの人が戸惑っていた。
People around were puzzled by his overly familiar behavior.
上司に対してあまり馴れ馴れしく接するのは避けた方がいい。
You should avoid being too familiar with your boss.