How to Cope With an Overzealous Tour Member
Book trips where multiple guides are present at all times. One is there to handle special situations just like this.
Talk to your guide, not to the traveler in question. Guides are trained to handle a variety of personalities.
Isolate the individual. That will only make him more likely to further monopolize your guide’s attention.
Be too quick to judge. As the group dynamic shakes out, needy travelers tend to settle down.