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
I'm referring to your man's inappropriate friend who hits on girls like an incurable sleaze. If you think your bridesmaids might feel uncomfortable, discuss with your fiance to see how you both want to handle it. You have to include him in this discussion, as the person in question is his friend 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.
See also: 11 wedding tasks you can entrust him with.
4. Seek help
If there's someone who you're closer to in your fiance's wedding party, seek his help to keep the troublemaker in check (when necessary).
See also: things brides do that drive grooms mad.
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. And even if anything negative happens on your big day, don't let it ruin your mood anyway.