The pub is crowded
You stay focused on the drinks you are making and ask for support from your colleague who is more inclined to handle this type of situation.
Without interrupting your service, you talk to one of the guy's friends explaining that you cannot serve his friend a drink. Alternatively, you offer him a non-alcoholic cocktail.
You offer him a non-alcoholic cocktail of your own invention so good that he will surely like it!
The bar is crowded