When people stumble over their words, they have a tendency to apologize. While I understand that they may feel embarrassed, I think that they would be better served by thanking people for being patient instead. Apologizing makes a conversation feel negative when in reality nothing bad happened, while appreciation feels positive.
Everyone experiences difficulty expressing themselves from time to time. It's perfectly normal. In fact, the act of apologizing makes the situation more awkward because your audience may start feeling the need to tell you that you don't need to apologize. On the other hand, when you say "thank you" people are more likely to say "you're welcome" and move on. Assume that people want you to succeed. By staying positive, you're more likely to have people rooting for you. Don't give your audience permission to look for your shortcomings.