The guard should politely escort Benjamin somewhere else before he gets violent or does things that he could do inebriated.
Step-by-step explanation:
The guard in this situation is not required to use force on Benjamin as he is yet to do something destructive to anything but is obviously not in the state of complete control over himself.
So the guard must go up to him and escort him away from the situation telling him that it is strictly not allowed to engage someone even in conversation when they are uncomfortable.
If this results in an altercation then the guard is free to use force on the person but not before this. He must however intervene.