I officiated a wedding last summer and spent an inordinate amount of time stressing over it. Catastrophizing each potential moment; each potential stutter. Truthfully, it went fine. Not perfect. Not awful. Perhaps the most helpful thought was that this couple asked me to officiate their special day. They knew I stuttered, but asked anyway. I’m a special part of their life not unlike how you are no doubt a special part of theirs. Remember that they asked you to be a best man because you are an incredibly valuable part of their life. Make the speech. It will go as it goes. Dance the night away. Don’t suffer imagined troubles.