Well there is a mitzvah to drink on Purim, but the rest of the year the klal dosent feel the same?? so seems that Purim is more lenient in some circumstances maybe by costumes is the same?
That said, the Mishna Berura is of the opinion that we should abolish this minhag, and perhaps if it is only one garment and the gender is clear we shouldnt protest. (read: we shouldnt burn garbage cans, throw rocks, or pour bleach on them.)
I dressed up my 2yo daughter like a boy. She wasn’t so happy to be wearing pants, but it was really cute and we have great pictures from it. We wouldn’t do it after age 3.
My brother was a girl last year (as I mentioned in another thread). He was nine. At above bar mitzvah he wouldn’t be allowed to do it (if he actually wanted to, that is…)
My dad’s friend was an Arab.
Personally, those are not the weirdest costumes I’ve ever heard of.
as an aside, my father dressed up one year as a woman. He wore a dress with a shaitel and put a pillow by his stomache. And he had a rather large moustache.