Answer to Question 1
Probably not. The John Nash character has not described a Nash equilibrium. In a Nash equilibrium, each player chooses a strategy that is a best response to the other players' strategies. If none of the other men have asked the beautiful woman to dance, then each of the men's best response is to ask her to dance. Perhaps the moral of the story is that Hollywood should not discuss economics and economists should not make movies.
Answer to Question 2
An externality is a benefit or cost that affects someone who is not directly involved in the production or consumption of a good or service.