Addressing it right in the meeting will derail the flow of the meeting and prevent you from achieving what you want to achieve. If Gary brings up things that were already discussed, you have to prevent people from rehashing everything that has been said for his benefit. After the meeting, I would talk with Gary how his behavior is not acceptable, and how he could be losing influence with others by trying to get away with behavior others do not think is right. Losing influence = losing opportunities, and share with Gary why influence is key for his career progression.