Alice and Betty are in an Improbably Female Cast where males are rare, if not entirely nonexistent, or Alice and Betty spend the whole movie facing a predicament that requires their full and immediate attention; for them to discuss men would be absurd and counterproductive.
Aaron and Bob have a conversation not about women.
Alternately, every conversation but one Alice and Betty have is about men.
Alternately, every conversation but one Alex and Bob have is about women.
A meta example, Bob Harrison invents "the Harrison Test" and in order to pass the story must three criteria: there are at least two men, they have at least one conversation, and it isn't about women. And this is often used to point out how men's lives seem to be defined by women in the movies.
Subverted: Alice and Betty have a long, fruitful and insightful conversation about a friend of theirs, with no gender pronouns given, only for the last sentence to reveal that they are talking about Bob...
Double Subverted: ...and it turns out that "Bob" is actually Roberta and uses the masculine nickname.
There are no women, there is only one woman, Alice and Betty never speak to one another, or Alice and Betty only discuss men.
All of the characters are genderless.
Enforced: The writer wants to create women who are as multidimensional as their male counterparts and so gives them dialogue unrelated to any man or male character.
"Rule Number One: Never discuss guys and romance, especially not in the same sentence".
Alice and Betty talk to each other about The Bechdel Test. They debate whether talking about it is sufficient to pass it.
Invoked: Alice and Betty have an important conversation because they refuse to be like the women on TV who only talk about men.
Exploited: Someone sticks a completely superfluous scene of two women talking into a work, and then brag about how feminist it is.
Defied: Alice and Betty talk about men because they refuse to be like the women on TV who believe talking about men is beneath them.
Discussed: "There's more to life than guys and romance, you know".
Conversed: "Is their refusal to talk about men supposed to be feminist? It seems odd when they have a mutual male friend".
Implied: Alice and Betty could not possibly have missed Donnie sitting just outside the door to the room where they had their conversation, but they act as if he isn't even there on their way out.
Deconstructed: Alice and Betty avoid discussing men, but it is revealed that they avoid the subject so completely because they both have some sort of psychological trauma related to men and that they cannot bear to relive it.
Reconstructed: They deal with their trauma through regular therapy practices and discuss men in a rational proportion to the rest of their lives.
Played For Laughs: Alice and Betty's conversation involves a witty, funny anecdote or observation.
Played For Drama: Alice and Betty's conversation means a lot to the plot and/or delves into Contemplate Our Navels territory.