Don't ever feel bad about it; at the end and of the day it is outside of our control. I understand what you mean, when a block slows down the flow of the conversation. Sometimes people do tend to switch off. All I can say is, be confident and try not to worry about what other people think. In my experience when you stop worrying and stop doubting yourself this is when we are most in control of our speech. If you do block on a word, just pause take a breath and say it again. Most people are very understanding and it's always better to pause stop and try again don't try to force the word out. This only exacerbates it. Ultimately confidence is the key it sounds cliche but in my opinion it's true and the most powerful thing that you can do is be confident even when you do stutter. For me this was a turning point, now I am not ashamed at all. This lack of shame and worry clears the mind. Which intern in my experience increases fluency.