When the Torah forbids a man to dress in women’s clothing (see 22:5) what is its intention? Is every situation of cross-dressing forbidden by the Torah, or is it only when there is a specific intent to mingle with members of the opposite sex for inappropriate purposes?
This question appears to be a point of disagreement between Rabbi Eliezer ben Ya’akov and the Tanna Kamma. Rabbi Eliezer ben Ya’akov forbids any situation in which a man dresses like a woman or a woman dresses like a man, while the Tanna Kamma objects that the Torah only forbids this in a situation of to’eva (an abomination), which would only occur if the purpose was to allow a man to sit among women or a woman to sit among men.
The Rambam seems to follow the opinion of Rabbi Eliezer ben Ya’akov, since he rules that this prohibition is not based on a concern with sexual impropriety, but rather is connected with issues of avoda zara (idol worship), which is the to’eva referred to in the Torah (see Rambam HaMitzvot Lo Ta’aseh 40).
One situation that the Gemara states specifically as being considered “women’s clothing” is shaving parts of the body like the underarms or pubic area. In fact, Rabbi Ḥiyya bar Abba quotes Rabbi Yoḥanan as ruling that such behavior is forbidden by the Torah and would make the man who shaved those areas of his body liable for malkot (lashes).
Still it should be noted that in the responsa (legal/religious response to a formalized question) the Ge’onim put forward that the definition of what is considered “men’s clothing” or “women’s clothing” is subjective, and therefore is dependent on time and place. Thus, if the accepted norms of a given community are for men to dress a certain way (to wear kilts, for example) or to act a certain way (to shave their underarms, for example), those behaviors would no longer be considered “women’s dress.”