Flatbusher
According to the Chinuch the main reason of the issur (wearing clothing of the opposite sex) is to prevent male/female mixing.
But as discussed, the poskim extend it to other areas, clearly to treat men and women differently and thus create boundaries that prevent pritzus.
I know frum men who go to nail salons. I have an issue with that. It is inherently a place reserved for women and thus against the spirit of the halacha.
Obviously societal norms play a role. If a frum Scot wore a kilt, that would be mutar. I would even guess that we may allow a frum asian girl in vietnam to wear those baggy pantaloons. (since they are tznius and the norm)
The question is, “how long does it take for something to be considered a societal norm before the halacha may change?”
I personally would want it to be universal (and not something inherently pritzusdik). If all american guys colored their hair then maybe I can see a posek reversing a previous opinion. But I may be wrong. It could be that once something is assur in a society, we don’t change it. (ie lo-plug)