There are many ways to express the idea of being "in disagreement" with someone or something. You might say that you have a different opinion, a contrasting viewpoint, or a divergent perspective. You could also describe the situation as being at odds, in opposition, or in conflict. If you reject someone's argument outright, you might use words like dispute, challenge, or refute. Alternatively, you could express uncertainty or skepticism by using phrases like not convinced or unconvinced. Finally, you could describe the level of disagreement by using adjectives like vehement, intense, or passionate. No matter what words you choose, the key is to express your disagreement clearly and effectively.