The phrase "was insincere" can have multiple antonyms, depending on the context. A few potential antonyms include "was genuine," "was sincere," "was honest," "was authentic," "was truthful," "was forthright," and "was candid." All of these antonyms describe a person who communicates their thoughts and feelings with honesty and integrity, without any hidden agenda or ulterior motives. Rather than being insincere or fake, these individuals express themselves genuinely and authentically, fostering meaningful connections and building trust with those around them. Choosing to embody these antonyms can lead to more positive relationships, greater emotional intelligence, and a deeper sense of personal fulfillment.