The problem is how politically charged the word 'sexist' is. I'm aware that the boring unemotional dictionary definition is treating someone differently on the basis of gender, but in reality if a guy is hanging out in a women's toilet its not generally seen as sexist/sexism to ask him to leave (even though this is discrimination on the basis of sex).
So labelling anything where two genders are treated differently as 'sexism' or 'sexist' I don't think actually matches the modern usage of the word. I think the difference is it's usually used in a negative connotation and the type of discrimination is seen as non-acceptable - for instance most people wouldn't call a girl-band or boy-band sexist because they select their members based on gender, while most would call an employer sexist if they had a generic business and tried to segregate their teams into single-gender teams. Most people still don't have a problem with boy bands (i.e. a male-only-team in a music workplace), thus not sexist, but do have a problem with male-only-teams in other workplaces, thus sexist.
> if a guy is hanging out in a women's toilet its not generally seen as sexist/sexism to ask him to leave (even though this is discrimination on the basis of sex)
Enforcing a rule isn’t discrimination. The rule itself may or may not be discrimination.
> Most people still don't have a problem with boy bands (i.e. a male-only-team in a music workplace), thus not sexist, but do have a problem with male-only-teams in other workplaces, thus sexist.
They get the label “boy band” after they form. If they were a mixed gender group (like a workplace) and kicked out a talented female musician because they wanted to be male-only, that would be sexist.
I don’t remember seeing rules in the dictionary definition, and I also struggle to believe that something can’t be sexist/sexism if the laws allow it. I think in the western world we would say that another country banning women from driving would be an example of sexism, albeit within the laws of the country.
Also, I hate to break the illusion for you, but boy bands are often planned as such and are manufactured by the record labels. It’s not a coincidence, for example, that the spice girls are all girls - that’s because they only auditioned girls because they were making the spice girls.
So labelling anything where two genders are treated differently as 'sexism' or 'sexist' I don't think actually matches the modern usage of the word. I think the difference is it's usually used in a negative connotation and the type of discrimination is seen as non-acceptable - for instance most people wouldn't call a girl-band or boy-band sexist because they select their members based on gender, while most would call an employer sexist if they had a generic business and tried to segregate their teams into single-gender teams. Most people still don't have a problem with boy bands (i.e. a male-only-team in a music workplace), thus not sexist, but do have a problem with male-only-teams in other workplaces, thus sexist.