sauce for the goose is sauce for the gander, what's

What is suitable for a woman is suitable for a man. The proverb is also occasionally used in non-sexist contexts.

That that's good sawce for a goose, is good for a gander. ‥This is a woman's Proverb.
[1670 J. Ray English Proverbs 98]

Sauce for a Goose is Sauce for a Gander.
[1692 R. L'estrange Fables of Aesop cccii.]

A proverb of large equity‥declares‥that ‘sauce for the goose is sauce for the gander’. This maxim is pleasant enough to the goose.
[1894 Blackmore Perly-cross III. v.]

To buttress his case, the Russian leader pointed out that NATO itself had recently insisted that Macedonia implement this same principle in behalf of its Albanian ethnic minority. What was sauce for the Albanian goose was sauce for the Baltic gander.
[2002 National Review 28 Jan. 39]

Related to: men and women

Bibliography of major proverb collections and works cited from modern editions is available here.

What applies to one applies to both, especially to both male and female. For example, After her husband went off with his fishing buddies for a week, she decided to take a vacation without him--what's sauce for the goose, you know. This proverbial expression, often shortened as in the example, was cited and described as "a woman's proverb" in John Ray's English Proverbs (1678).