1. superlative form of insincere; most lacking in honesty, genuineness, or truthfulness
Usage: superlative degree; formal register

Examples

• His insincerest apology came only after he was caught red-handed.
• Of all the candidates, she gave the insincerest speech, reading from a script without any emotion.
• The insincerest compliments are often the easiest to spot.
• He wore his insincerest smile when greeting his rival at the event.
• That was the insincerest promise I have ever heard from a politician.
• Her insincerest tone made it clear she did not believe what she was saying.