Maybe the title is link bait, but I don't think this is "sexism" by definition. Sexism: "Prejudice, stereotyping, or discrimination, typically against women, on the basis of sex." A bunch of males were hitting on the author, crassly or awkwardly, but they were not denying the author equal rights. If a female asked a male to show their privates, no one would call it "sexism"; it might be rude, uncalled for, or strange…
The idea that a woman would 'show her tits' in public or private to a strange man when asked in public smacks me as sexist. Who ever created the score sheet where one of the goals was to 'get a woman to show her tits' shows an objectification of woman as purely sexual objects. This disadvantages 50% of the population based on their mammary glands.
It is a fact that men and woman flirt, it's one of the most exciting things that can happen, when two people click its quite frankly amazing.
This needs to be separated from pure objectification of anyone. If it were woman asking to see men's gonads many many men would feel deeply uncomfortable surrounded by woman with an expectation of a show and an implicit questioning/judging of the quality of their sack.