1. Doubt your honesty: When a man says "you're not honest," he may be questioning whether what you say or do is true and reliable, and he may believe that you are hiding or deceiving in certain situations.
2. Point out your irregular behavior: This sentence may also be used to point out that your behavior does not conform to social norms or expectations, such as being too frivolous, untrustworthy, or not steady enough.
3. Expressing dissatisfaction or disappointment: In a certain situation, this sentence may be a direct reaction to your behavior or attitude, expressing his dissatisfaction or disappointment towards you and hoping that you can make some changes.