How to determine common practice for halachos that are impacted by it

Question

Certain halachic issues are informed or even determined by the social standards of the (non-Jewish) society in which one lives. Examples include what falls under the prohibition of cross-dressing (see Rambam Avodas Kochavim 12:10, Shulchan Aruch Yoreh Deah 182) and standards of modesty that extend beyond the letter of the law (e.g. where it is socially unacceptable for a woman to go out without a veil, it might be halachically required for a Jewish woman to adhere to this standard of modesty beyond the basic objective halachic requirements - see http://hebrewbooks.org/rambam.aspx?sefer=4&hilchos=22&perek=13&halocha=11&hilite=).

My question is: what is considered "common practice" for the purposes of such halachos? How common does the practice have to be to permit it? Does it have to be done by the majority of people, enough people that you won't get weird looks if you do it, a minority of people that will nevertheless not be viewed as, for example, cross-dreessers for wearing a certain article of clothing, etc.?

Answer 1

Different halachos which depend upon social standards would use different standards...

Bishul Ma'achal Ben Drosai is a standard to determine whether something is cooked enough for Shabbos, and Ben Drosai was a single person (or a small group of crooks) who ate blue-rare meat!

Conversely, Mishamer only applies if the drink isn't considered potable by the majority of the world (not just Jews).

Tznius is based on Da'as Yehudis - standards of observant Jewish women, etc.

The status of an anusah from an unknown assailant is judged by either the majority of the local population or the majority of those who would be me'anes. (It's a machlokes in the Gemara, but I believe R'Moshe holds the latter).

Basically, there is no "common practice," and Chazal determines what the appropriate context for determining the standard is.