#1 THINK ABOUT THE ISSUE AT HAND
What's bothering you, really? Is it the way he's desperately trying to find someone, or you think he's a bad influence on your man by introducing him to new bad habits?
Think about it. If you think the problem's a minor one and can be overlooked, leave it.
#2 IF THE ISSUE'S SERIOUS, TALK TO YOUR FIANCE ABOUT IT
If the problem stems from his behaviour rather than his personality, you'll have to speak to your partner.
We're referring to your man's inappropriate friend who has a rep for hitting on ladies, or one who's known to act rashly or violently after a couple of drinks. If you think your bridesmaids might feel uncomfortable or it could lead to wedding day drama, respectfully and calmly (and in a non-accusatory manner) discuss it with your fiance to see how you both want to handle it.
You have to include your spouse-to-be in this discussion, as the person in question is his friend (and possibly a close one at that) after all. The one rule here? Never ever act alone, or worse, go behind his back to deal with the situation yourself.
#3 LET YOUR FIANCE HANDLE IT
Just as he lets you handle all the things you'll need for your bridesmaids, you can also leave him to take care of all the things he'll need his groomsmen to do. If there are concerns regarding his behaviour or what he might be saying during the speech, just let your fiance know about them, and trust him to handle it accordingly.
#4 SEEK HELP
If there's someone who you're closer to in your fiance's wedding party, seek his help to keep the particular groomsman in check (when necessary).
#5 DON'T DEMOTE HIM
Whatever it is, don't unask him to be a part of your wedding party. It's bad form, and surely you can tolerate him for a day?
#6 LEAVE IT
At the end of the day, you'll be marrying your fiance, and not the groomsman in question. Try not to dwell on it and don't spend too much time around that person - it'll distant you from what you find off-putting about their behaviour.
And even if anything negative happens on your big day, try not to let it ruin your mood anyway.