Will God hold me accountable for an ordinary word by which I intend to insult a specific person, even if people are unaware of my intentions?

It is clear that you have many (waswas) evil whisperings. Therefore, turn away from them and do not pay attention to them, for that is an effective cure for them. What you find in yourself, regarding the intention to insult, is due to the effect of these whisperings and does not result in harm to anyone. Consequently, there is no sin upon you.