I would really prefer if my friend's friend didn't to come with us on this vacation.
Why would you not want them to join you for the holiday?
I had a bad experience with his friend
You should just be honest and let your friend know you don't really like that person and you don't want that person to join. You just want to have your closest buddies go on this Holiday. Otherwise, you will not be happy during the holiday if that person tags along.
I really just don't want him to go.
If it's a holiday meant for you and your closest friends, then that should be all that gets invited. This other guy seems like more of an outsider to your group so your friend should be okay with him not coming. Just make sure you're honest with them about how you feel.